# Geometry

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

• ##### Introduction to Angles
Salman Khan

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

• ##### Angles Part 2
Salman Khan

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

• ##### Angles Part 3
Salman Khan

Angles formed when a transversal intersects parallel lines.

• ##### Angles Formed Between Transversals and Parallel Lines
Salman Khan

Angles of parallel lines.

• ##### Angles of Parallel Lines 2
Salman Khan

Angles of parallel lines examples.

• ##### The Angle Game
Salman Khan

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

• ##### Similar Triangles
Salman Khan

Introduction to similar triangles.

• ##### Similar Triangles 2
Salman Khan

More on similar triangles.

• ##### Area and Perimeter
Salman Khan

Area of rectangles and triangles. Perimeter of rectangles.

• ##### Circles: Radius, Diameter, and Circumference
Salman Khan

Understanding the relationship between the radius diameter and circumference of a circle.

• ##### The Pythagorean Theorem
Salman Khan

Introduction to the Pythagorean Theorem.

• ##### The Pythagorean Theorem II
Salman Khan

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

• ##### 45-45-90 Triangles
Salman Khan

Introduction to 45-45-90 Triangles.

• ##### Intro to 30-60-90 Triangles
Salman Khan

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

• ##### 30-60-90 Triangles II
Salman Khan

More examples using 30-60-90 triangles.

• ##### Heron's Formula
Salman Khan

Using Heron's Formula to determine the area of a triangle while only knowing the lengths of the sides.

• ##### Part 1 of Proof of Heron's Formula
Salman Khan

Part 1 of the proof of Heron's Formula.

• ##### Part 2 of Proof of Heron's Formula
Salman Khan

Showing that the expression in part 1 is identical to Heron's Formula.

• ##### An Inscribed Angle is Half of a Central Angle that Subtends the Same Arc
Salman Khan

Showing that an inscribed angle is half of a central angle that subtends the same arc.

• ##### Area of Inscribed Equilateral Triangle (Some Basic Trig Used) 2
Salman Khan

Problem that requires us to figure out the area of an equilateral triangle inscribed in a circle (A little trigonometry used).

• ##### Right Triangles Inscribed in Circles
Salman Khan

Proof showing that a triangle inscribed in a circle having a diameter as one side is a right triangle.

• ##### Area of Inscribed Equilateral Triangle (Some Basic Trig Used)
Salman Khan

Area of Diagonal Generated Triangles of Rectangle are Equal.