# Geometry

#### Learn about shapes and their properties such as size and position. Created by Khan Academy.Recommended that you have a good foundation in Algebra before taking this course.

20 hours

Intermediate

##### Pick a lesson

1: Euclid as the Father of Geometry
2: Language and Notation of Basic Geometry
3: Lines, Line Segments, and Rays
4: Language and Notation of the Circle
5: Angle Basics
6: Measuring Angles in Degrees
7: Using a Protractor
8: Measuring Angles
9: Complementary and Supplementary Angles
10: Angles at the intersection of two lines
11: Proof-Vertical Angles are Equal
12: Angles Formed by Parallel Lines and Transversals
13: Proof - Sum of Measures of Angles in a Triangle are 180
14: Triangle Angle Example 1
15: Triangle Angle Example 2
16: Triangle Angle Example 3
17: Challenging Triangle Angle Problem
18: Proof - Corresponding Angle Equivalence Implies Parallel Lines
19: Finding more angles
20: Sum of Interior Angles of a Polygon
21: Congruent Triangles and SSS
22: SSS to Show a Radius is Perpendicular to a Chord that it Bisects
23: Other Triangle Congruence Postulates
24: Two column proof showing segments are perpendicular
25: Sum of the exterior angles of convex polygon
26: Finding Congruent Triangles
27: More on why SSA is not a postulate
28: Congruent Triangle Proof Example
29: Congruent Triangle Example 2
30: Congruent legs and base angles of Isosceles Triangles
31: Equilateral Triangle Sides and Angles Congruent
32: Equilateral and Isosceles Example Problems
33: Another Isosceles Example Problem
34: Example involving an isosceles triangle and parallel lines
35: Figuring out all the angles for congruent triangles example
36: Perimeter and Area Basics
37: Triangle Area Proofs
38: Interesting Perimeter and Area Problems
39: Koch Snowflake Fractal
40: Area of an Equilateral Triangle
41: Area of Koch Snowflake (part 1) - Advanced
42: Area of Koch Snowflake (part 2) - Advanced
43: Challenging Perimeter Problem
44: Similar Triangle Basics
45: Similarity Postulates
46: Similar Triangle Example Problems
47: Similarity Example Problems
48: Challenging Similarity Problem
49: Similarity example where same side plays different roles
50: Finding Area Using Similarity and Congruence
51: Pythagorean Theorem Proof Using Similarity
52: 30-60-90 Triangle Side Ratios Proof
53: 45-45-90 Triangle Side Ratios
54: 30-60-90 Triangle Example Problem
55: The Golden Ratio
56: Introduction to angles
57: Angles (part 2)
58: Angles (part 3)
59: Angles formed between transversals and parallel lines
60: Angles of parallel lines 2
61: The Angle Game
62: Similar triangles
63: Similar triangles (part 2)
64: Angle Game (part 2)
65: Acute Right and Obtuse Angles
66: Area and Perimeter
67: Circles: Radius, Diameter and Circumference
68: Area of a circle
69: The Pythagorean Theorem
70: Pythagorean Theorem II
71: 45-45-90 Triangles
72: Intro to 30-60-90 Triangles
73: 30-60-90 Triangles II
74: Solid Geometry Volume
75: Cylinder Volume and Surface Area
76: Heron's Formula
77: Part 1 of Proof of Heron's Formula
78: Part 2 of the Proof of Heron's Formula
79: Inscribed and Central Angles
80: Area of Inscribed Equilateral Triangle (some basic trig used)
81: Right Triangles Inscribed in Circles (Proof)
82: Area of Diagonal Generated Triangles of Rectangle are Equal
83: Triangle Medians and Centroids
84: Triangle Medians and Centroids (2D Proof)
85: Rhombus Diagonals
86: 2003 AIME II Problem 7
87: Perpendicular Radius Bisects Chord
88: Circumcenter of a Triangle
89: Circumcenter of a Right Triangle
90: Three Points Defining a Circle
91: Point Line Distance and Angle Bisectors
92: Incenter and incircles of a triangle
93: Angle Bisector Theorem Proof
94: Inradius Perimeter and Area
95: Angle Bisector Theorem Examples
96: Medians divide into smaller triangles of equal area
97: Exploring Medial Triangles
98: Proving that the Centroid is 2-3rds along the Median
99: Median Centroid Right Triangle Example
100: Proof - Triangle Altitudes are Concurrent (Orthocenter)
101: Review of Triangle Properties
102: Euler Line
103: Euler's Line Proof
104: Common Orthocenter and Centroid