geometry khanacademy 5/5 (1)

Geometry - Khan Academy FREE

URL

HTML code

reported by Khan_academy (19 courses)

updated 11/04/2015

59,695 views

claim ownership

Videos on geometry. Basic understanding of Algebra I necessary. After this, you'll be ready for Trigonometry.

Geometry on Khan Academy: We are surrounded by space. And that space contains lots of things. And these things have shapes. In geometry we are concerned with the nature of these shapes, how we define them, and what they teach us about the world at large--from math to architecture to biology to astronomy (and everything in between). Learning geometry is about more than just taking your medicine ("It's good for you!"), it's at the core of everything that exists--including you. Having said all that, some of the specific topics we'll cover include angles, intersecting lines, right triangles, perimeter, area, volume, circles, triangles, quadrilaterals, analytic geometry, and geometric constructions. Wow. That's a lot. To summarize: it's difficult to imagine any area of math that is more widely used than geometry.

About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content.

For free. For everyone. Forever. #YouCanLearnAnything

Subscribe to Khan Academy’s Geometry channel:
www.youtube.com/channel/UCD3OtKx...ion=1
Subscribe to Khan Academy: www.youtube.com/subscription_cen...ademy

Lessons
1) Euclid as the father of geometry \| Introduction to Euclidean geometry \| Geometry We don't normally delve too far into history when talking about math, but sometimes it's important to have perspective about how some of our math concepts came about and how influential they have beco ... 482 views watch video
2) Basic geometry: language and labels \| Introduction to Euclidean geometry \| Geometry Before learning any new concept (mathematical or otherwise), it's important we learn and use a common language and label concepts consistently. 598 views watch video
3) Intro to lines, line segments, and rays \| Geometry Let's get familiar with the difference between lines, line segments, and rays. Hint: a ray is somewhere between a line and a line segment! Practice this lesson yourself on KhanAcademy.org right now: ... 588 views watch video
4) Language and notation of the circle \| Introduction to Euclidean geometry \| Geometry Formal definition of a circle. Tangent and secant lines. Diameters and radii. major and minor arcs 580 views watch video
5) Angle basics \| Angles and intersecting lines \| Geometry The naming of an angle is related to the line segments that create it. We'll also learn about the angle's vertex. Come on. Let's do this. 626 views watch video
6) Measuring angles in degrees \| Angles and intersecting lines \| Geometry Let's come up with an exact way to measure an angle using a protractor. We'll also learn about acute angles. Not to be confused with augly angles :) 551 views watch video
7) Measuring angles using a protractor \| Angles and intersecting lines \| Geometry Let's use our virtual protractor to measure some angles together, shall we? 620 views watch video
8) More angle measurements using a protractor \| Angles and intersecting lines \| Geometry We're practicing measuring angles using the virtual protractor. Do this a few times with us and you'll use a real protractor like a pro! Practice this lesson yourself on KhanAcademy.org right now: ... 488 views watch video
9) Complementary and supplementary angles \| Angles and intersecting lines \| Geometry Let's add some tools to our geometry tool belt. Here's a thorough explanation of complementary and supplementary angles, as well as definitions of adjacent and straight angles. Practice this lesson y ... 535 views watch video
10) Introduction to vertical angles \| Angles and intersecting lines \| Geometry By using our knowledge of supplementary, adjacent, and vertical angles, we can solve problems involving the intersection of two lines. Including this one! Practice this lesson yourself on KhanAcademy ... 510 views watch video
11) Proof: Vertical angles are equal \| Angles and intersecting lines \| Geometry Proving that vertical angles are equal Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 520 views watch video
12) Angles formed by parallel lines and transversals \| Geometry Parallel lines, transversal lines, corresponding angles Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 642 views watch video
13) Proof - Sum of Measures of Angles in a Triangle are 180 Proof that the sum of the measures of the angles in a triangle are 180 728 views watch video
14) Triangle angle example 1 \| Angles and intersecting lines \| Geometry Figuring out angles in a triangle. A little about exterior angles being the sum of the remote interior angles 591 views watch video
15) Triangle angle example 2 \| Angles and intersecting lines \| Geometry Another example finding angles in triangles 610 views watch video
16) Triangle angle example 3 \| Angles and intersecting lines \| Geometry Multiple ways to solve for the angles of multiple triangles 611 views watch video
17) Challenging triangle angle problem \| Angles and intersecting lines \| Geometry Interesting problem finding the sums of particular exterior angles of an irregular pentagon 737 views watch video
18) Proof: Corresponding angle equivalence implies parallel lines \| Geometry Proof by contradiction that corresponding angle equivalence implies parallel lines 641 views watch video
19) Finding more angles \| Angles and intersecting lines \| Geometry Example of angle hunting! Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 667 views watch video
20) Sum of interior angles of a polygon \| Angles and intersecting lines \| Geometry Showing a generalized way to find the sum of the interior angles of any polygon Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 641 views watch video
21) Congruent triangles and SSS \| Congruence \| Geometry What it means for triangles to be congruent 710 views watch video
22) SSS to show a radius is perpendicular to a chord that it bisects \| Geometry More on the difference between a theorem and axiom. Proving a cool result using SSS 729 views watch video
23) Other triangle congruence postulates \| Congruence \| Geometry SSS, SAS, ASA and AAS postulates for congruent triangles. Showing AAA is only good for similarity and SSA is good for neither 757 views watch video
24) Two column proof showing segments are perpendicular \| Congruence \| Geometry Using triangle congruency postulates to show that two intersecting segments are perpendicular 627 views watch video
25) Sum of the exterior angles of convex polygon \| Geometry More elegant way to find the sum of the exterior angles of a convex polygon 579 views watch video
26) Finding congruent triangles \| Congruence \| Geometry Using the SSS, ASA, SAS, and AAS postulates to find congruent triangles Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 601 views watch video
27) More on why SSA is not a postulate \| Congruence \| Geometry SSA special cases including RSH 589 views watch video
28) Congruent triangle proof example \| Congruence \| Geometry Proving that a point is the midpoint via triangle congruency 531 views watch video
29) Congruent triangle example 2 \| Congruence \| Geometry Showing that segments have the same length 540 views watch video
30) Congruent legs and base angles of isosceles triangles \| Congruence \| Geometry Showing that congruent legs imply equal base angles and vice versa Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 698 views watch video
31) Equilateral triangle sides and angles congruent \| Congruence \| Geometry Showing that all of the angles of an equilateral triangle are 60 degrees Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 657 views watch video
32) Equilateral and isosceles example problems \| Congruence \| Geometry Three example problems involving isosceles and equilateral triangles. 2 from Art of Problem Solving (by Richard Rusczyk) book Practice this lesson yourself on KhanAcademy.org right now: https://www ... 602 views watch video
33) Another isosceles example problem \| Congruence \| Geometry Possible angles for an isosceles triangle 564 views watch video
34) Example involving an isosceles triangle and parallel lines \| Congruence \| Geometry Integrating what we know about isosceles triangles and parallel lines 519 views watch video
35) Figuring out all the angles for congruent triangles example \| Congruence \| Geometry Another example of using congruency to figure out a bunch of angles 638 views watch video
36) Perimeter and area: the basics \| Perimeter, area, and volume \| Geometry Great geometry primer on perimeter and area. Listen carefully. Sal explains the concepts so you'll understand them. Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacade ... 558 views watch video
37) Triangle area proofs \| Perimeter, area, and volume \| Geometry Proving that the area of any triangle is 1/2 b x h Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 635 views watch video
38) Interesting perimeter and area problems \| Perimeter, area, and volume \| Geometry Three example problems involving perimeter and area 635 views watch video
$Koch snowflake fractal \| Perimeter, area, and volume \| Geometry$ 39) Koch snowflake fractal \| Perimeter, area, and volume \| Geometry A shape that has an infinite perimeter but finite area 557 views watch video
40) Area of an equilateral triangle \| Perimeter, area, and volume \| Geometry Finding the formula for the area of an equilateral triangle with side s 535 views watch video
41) Area of Koch snowflake (part 1) - advanced \| Perimeter, area, and volume \| Geometry Starting to figure out the area of a Koch Snowflake (which has an infinite perimeter) 601 views watch video
42) Area of Koch snowflake (part 2) - advanced \| Perimeter, area, and volume \| Geometry Summing an infinite geometric series to finally find the finite area of a Koch Snowflake 497 views watch video
43) Challenging perimeter problem \| Perimeter, area, and volume \| Geometry Perimeter of rectangle covered by 9 non-overlapping squares. From 2000 American Invitational Math Exam 589 views watch video
44) Similar triangle basics \| Similarity \| Geometry Introduction to what it means for triangles to be similar Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 585 views watch video
45) Similarity postulates \| Similarity \| Geometry Thinking about what we need to know to determine whether two triangles are similar Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 479 views watch video
46) Similar triangle example problems \| Similarity \| Geometry Multiple examples looking for similarity of triangles Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 715 views watch video
47) Similarity example problems \| Similarity \| Geometry Two example problems involving similarity Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 565 views watch video
48) Challenging similarity problem \| Similarity \| Geometry Interesting similarity problem where we don't have a lot of information to work with Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 508 views watch video
49) Similarity example where same side plays different roles \| Similarity \| Geometry The same side not corresponding to itself in two similar triangles Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 512 views watch video
50) Finding area using similarity and congruence \| Similarity \| Geometry Example of using similarity and congruence to find the area of a triangle Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 510 views watch video
51) Pythagorean theorem proof using similarity \| Geometry Proof of the Pythagorean Theorem using similarity Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 517 views watch video
52) 30-60-90 triangle side ratios proof \| Right triangles and trigonometry \| Geometry Proving the ratios between the sides of a 30-60-90 triangle 712 views watch video
53) 45-45-90 triangle side ratios \| Right triangles and trigonometry \| Geometry Showing the ratios of the sides of a 45-45-90 triangle are 1:1:sqrt(2) 627 views watch video
54) 30-60-90 triangle example problem \| Right triangles and trigonometry \| Geometry Using what we know about 30-60-90 triangles to solve what at first seems to be a challenging problem Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/g ... 711 views watch video
55) The golden ratio \| Introduction to Euclidean geometry \| Geometry An introduction to one of the most amazing ideas/numbers in mathematics 584 views watch video
56) Introduction to angles (old) \| Angles and intersecting lines \| Geometry What an angle is. Angles in a circle. Complementary and supplementary angles. 664 views watch video
57) Angles (part 2) \| Angles and intersecting lines \| Geometry More on complementary and supplementary angles. Introduction to opposite angles. 637 views watch video
58) Angles (part 3) \| Angles and intersecting lines \| Geometry Angles formed when a transversal intersects parallel lines. 659 views watch video
59) Angles formed between transversals and parallel lines \| Geometry Angles of parallel lines 589 views watch video
60) Angles of parallel lines 2 \| Angles and intersecting lines \| Geometry Angles of parallel lines examples 430 views watch video
61) The angle game \| Angles and intersecting lines \| Geometry Using what we know to solve for angles in the Angle Game. 600 views watch video
62) Similar triangles \| Similarity \| Geometry Introduction to similar triangles 516 views watch video
63) Similar triangles (part 2) \| Similarity \| Geometry More on similar triangles 707 views watch video
64) Angle game (part 2) \| Angles and intersecting lines \| Geometry More examples of the Angle Game. 639 views watch video
65) Acute right and obtuse angles \| Angles and intersecting lines \| Geometry We briefly discussed the types of angles in the last tutorial but we'll delve a little deeper into acute, obtuse, and right angles here. Practice this lesson yourself on KhanAcademy.org right now: ... 613 views watch video
66) Area and Perimeter Area of rectangles and triangles. Perimeter of rectangles. 626 views watch video
67) Circles: radius, diameter, circumference and Pi \| Geometry A circle is at the foundation of geometry and how its parts relate to each other is both completely logical and a wonder. Practice this lesson yourself on KhanAcademy.org right now: https://www.k ... 551 views watch video
68) Area of a circle Area of a circle and how it relates to radius and diameter 631 views watch video
69) The Pythagorean theorem intro \| Right triangles and trigonometry \| Geometry Introduction to the Pythagorean Theorem Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 666 views watch video
70) Pythagorean theorem II \| Right triangles and trigonometry \| Geometry More Pythagorean Theorem examples. Introduction to 45-45-90 triangles. 614 views watch video
71) 45-45-90 triangles \| Right triangles and trigonometry \| Geometry Introduction to 45-45-90 Triangles 670 views watch video
72) Intro to 30-60-90 triangles \| Right triangles and trigonometry \| Geometry A few more 45-45-90 examples and an introduction to 30-60-90 triangles. 469 views watch video
73) 30-60-90 Triangles II More examples using 30-60-90 triangles. More free lessons at: http://www.khanacademy.org/video?v=3mLUJ 554 views watch video
74) Find the volume of a triangular prism and cube \| Geometry In this tutorial we'll practice finding solid geometry volume. Keep paper and pencil nearby in case you want to remember the formulas. Practice this lesson yourself on KhanAcademy.org right now: ... 579 views watch video
75) Cylinder volume and surface area \| Perimeter, area, and volume \| Geometry Finding the volume and surface area of a cylinder Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 625 views watch video
76) Heron's formula \| Perimeter, area, and volume \| Geometry Using Heron's Formula to determine the area of a triangle while only knowing the lengths of the sides 562 views watch video
77) Part 1 of proof of Heron's formula \| Perimeter, area, and volume \| Geometry Part 1 of the proof of Heron's Formula 575 views watch video
78) Part 2 of proof of Heron's formula \| Perimeter, area, and volume \| Geometry Showing that the expression in part 1 is identical to Heron's Formula 652 views watch video
79) Inscribed and central angles \| Circles \| Geometry Showing that an inscribed angle is half of a central angle that subtends the same arc Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 779 views watch video
80) Area of inscribed equilateral triangle (some basic trig used) \| Circles \| Geometry Problem that requires us to figure out the area of an equilateral triangle inscribed in a circle (A little trigonometry used) 513 views watch video
81) Right Triangles Inscribed in Circles (Proof) Proof showing that a triangle inscribed in a circle having a diameter as one side is a right triangle 702 views watch video
82) Area of diagonal generated triangles of rectangle are equal \| Geometry Area of Diagonal Generated Triangles of Rectangle are Equal 508 views watch video
83) Triangle medians and centroids \| Special properties and parts of triangles \| Geometry Seeing that the centroid is 2/3 of the way along every median 500 views watch video
84) Triangle medians and centroids (2D proof) \| Geometry Showing that the centroid is 2/3 of the way along a median 551 views watch video
85) Rhombus diagonals \| Quadrilaterals \| Geometry Proof that the diagonals of a rhombus are perpendicular bisectors of each other 596 views watch video
86) 2003 AIME II problem 7 \| Special properties and parts of triangles \| Geometry 538 views watch video
87) Perpendicular radius bisects chord \| Congruence \| Geometry Simple proof using RSH postulate to show that a radius perpendicular to a chord bisects it 651 views watch video
88) Circumcenter of a triangle \| Special properties and parts of triangles \| Geometry Multiple proofs showing that a point is on a perpendicular bisector of a segment if and only if it is equidistant from the endpoints. Using this to establish the circumcenter, circumradius, and circum ... 545 views watch video
89) Circumcenter of a right triangle \| Geometry Showing that the midpoint of the hypotenuse is the circumcenter 533 views watch video
90) Three points defining a circle \| Special properties and parts of triangles \| Geometry Three points uniquely define a circle. The center of a circle is the circumcenter of any triangle the circle is circumscribed about. 535 views watch video
91) Point-line distance and angle bisectors \| Geometry Thinking about the distance between a point and a line. Proof that a point on an angle bisector is equidistant to the sides of the angle and a point equidistant to the sides is on an angle bisector 427 views watch video
92) Incenter and incircles of a triangle \| Geometry Using angle bisectors to find the incenter and incircle of a triangle 472 views watch video
93) Angle bisector theorem proof \| Special properties and parts of triangles \| Geometry What the angle bisector theorem is and its proof 731 views watch video
94) Inradius, perimeter, and area \| Special properties and parts of triangles \| Geometry Showing that area is equal to inradius times semiperimeter 575 views watch video
95) Angle bisector theorem examples \| Geometry Using the angle bisector theorem to solve for sides of a triangle Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ... 902 views watch video
96) Medians divide into smaller triangles of equal area \| Geometry Showing that the three medians of a triangle divide it into six smaller triangles of equal area. Brief discussion of the centroid as well 540 views watch video
97) Exploring medial triangles \| Special properties and parts of triangles \| Geometry What a medial triangle is and its properties 597 views watch video
98) Proving that the centroid is 2-3rds along the median \| Geometry Showing that the centroid divides each median into segments with a 2:1 ratio (or that the centroid is 2/3 along the median) 476 views watch video
99) Median centroid right triangle example \| Geometry Example involving properties of medians 756 views watch video
100) Proof: Triangle altitudes are concurrent (orthocenter) \| Geometry Showing that any triangle can be the medial triangle for some larger triangle. Using this to show that the altitudes of a triangle are concurrent (at the orthocenter). 504 views watch video

Load all results

Follow this course

Votes
Open Discussions

Name

Comment (optional)

Click on the star to vote

Correlated course

Languages Oneworlditaliano 5031 views

Web Stats

Community: 17,009 users
Active courses: 74,474
Lessons: 2,066,701
Data: 74 GB
Online: 49 users

Geometry - Khan Academy FREE

Lessons

We don't normally delve too far into history when talking about math, but sometimes it's important to have perspective about how some of our math concepts came about and how influential they have beco ...

Before learning any new concept (mathematical or otherwise), it's important we learn and use a common language and label concepts consistently.

Let's get familiar with the difference between lines, line segments, and rays. Hint: a ray is somewhere between a line and a line segment! Practice this lesson yourself on KhanAcademy.org right now: ...

Formal definition of a circle. Tangent and secant lines. Diameters and radii. major and minor arcs

The naming of an angle is related to the line segments that create it. We'll also learn about the angle's vertex. Come on. Let's do this.

Let's come up with an exact way to measure an angle using a protractor. We'll also learn about acute angles. Not to be confused with augly angles :)

Let's use our virtual protractor to measure some angles together, shall we?

We're practicing measuring angles using the virtual protractor. Do this a few times with us and you'll use a real protractor like a pro! Practice this lesson yourself on KhanAcademy.org right now: ...

Let's add some tools to our geometry tool belt. Here's a thorough explanation of complementary and supplementary angles, as well as definitions of adjacent and straight angles. Practice this lesson y ...

By using our knowledge of supplementary, adjacent, and vertical angles, we can solve problems involving the intersection of two lines. Including this one! Practice this lesson yourself on KhanAcademy ...

Proving that vertical angles are equal Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

Parallel lines, transversal lines, corresponding angles Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

Proof that the sum of the measures of the angles in a triangle are 180

Figuring out angles in a triangle. A little about exterior angles being the sum of the remote interior angles

Another example finding angles in triangles

Multiple ways to solve for the angles of multiple triangles

Interesting problem finding the sums of particular exterior angles of an irregular pentagon

Proof by contradiction that corresponding angle equivalence implies parallel lines

Example of angle hunting! Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

Showing a generalized way to find the sum of the interior angles of any polygon Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

What it means for triangles to be congruent

More on the difference between a theorem and axiom. Proving a cool result using SSS

SSS, SAS, ASA and AAS postulates for congruent triangles. Showing AAA is only good for similarity and SSA is good for neither

Using triangle congruency postulates to show that two intersecting segments are perpendicular

More elegant way to find the sum of the exterior angles of a convex polygon

Using the SSS, ASA, SAS, and AAS postulates to find congruent triangles Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

SSA special cases including RSH

Proving that a point is the midpoint via triangle congruency

Showing that segments have the same length

Showing that congruent legs imply equal base angles and vice versa Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

Showing that all of the angles of an equilateral triangle are 60 degrees Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

Three example problems involving isosceles and equilateral triangles. 2 from Art of Problem Solving (by Richard Rusczyk) book Practice this lesson yourself on KhanAcademy.org right now: https://www ...

Possible angles for an isosceles triangle

Integrating what we know about isosceles triangles and parallel lines

Another example of using congruency to figure out a bunch of angles

Great geometry primer on perimeter and area. Listen carefully. Sal explains the concepts so you'll understand them. Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacade ...

Proving that the area of any triangle is 1/2 b x h Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

Three example problems involving perimeter and area

A shape that has an infinite perimeter but finite area

Finding the formula for the area of an equilateral triangle with side s

Starting to figure out the area of a Koch Snowflake (which has an infinite perimeter)

Summing an infinite geometric series to finally find the finite area of a Koch Snowflake

Perimeter of rectangle covered by 9 non-overlapping squares. From 2000 American Invitational Math Exam

Introduction to what it means for triangles to be similar Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

Thinking about what we need to know to determine whether two triangles are similar Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

Multiple examples looking for similarity of triangles Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

Two example problems involving similarity Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

Interesting similarity problem where we don't have a lot of information to work with Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

The same side not corresponding to itself in two similar triangles Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

Example of using similarity and congruence to find the area of a triangle Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

Proof of the Pythagorean Theorem using similarity Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

Proving the ratios between the sides of a 30-60-90 triangle

Showing the ratios of the sides of a 45-45-90 triangle are 1:1:sqrt(2)

Using what we know about 30-60-90 triangles to solve what at first seems to be a challenging problem Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/g ...

An introduction to one of the most amazing ideas/numbers in mathematics

What an angle is. Angles in a circle. Complementary and supplementary angles.

More on complementary and supplementary angles. Introduction to opposite angles.

Angles formed when a transversal intersects parallel lines.

Angles of parallel lines

Angles of parallel lines examples

Using what we know to solve for angles in the Angle Game.

Introduction to similar triangles

More on similar triangles

More examples of the Angle Game.

We briefly discussed the types of angles in the last tutorial but we'll delve a little deeper into acute, obtuse, and right angles here. Practice this lesson yourself on KhanAcademy.org right now: ...

Area of rectangles and triangles. Perimeter of rectangles.

A circle is at the foundation of geometry and how its parts relate to each other is both completely logical and a wonder. Practice this lesson yourself on KhanAcademy.org right now: https://www.k ...

Area of a circle and how it relates to radius and diameter

Introduction to the Pythagorean Theorem Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/geome ...

More Pythagorean Theorem examples. Introduction to 45-45-90 triangles.

Introduction to 45-45-90 Triangles

A few more 45-45-90 examples and an introduction to 30-60-90 triangles.

More examples using 30-60-90 triangles. More free lessons at: http://www.khanacademy.org/video?v=3mLUJ

In this tutorial we'll practice finding solid geometry volume. Keep paper and pencil nearby in case you want to remember the formulas. Practice this lesson yourself on KhanAcademy.org right now: ...