Search "geometry"

Complementary and supplementary angles

Basics of complementary, supplementary, adjacent and straight angles. Also touching on what it means to be perpendicular

Khan Academy

Acute right and obtuse angles

The difference between acute, obtuse and right angles

Measuring angles

Using the KA virtual protractor to measure angles

Measuring angles in degrees

How to measure an angle in degrees

Angle basics

Definition of an angle. How to denote an angle using points on the angle (including the vertex)

Language and notation of the circle

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

Euclid as the father of geometry

Euclid and his Elements (and how much Abraham Lincoln liked them)

Solid geometry volume

Volume of triangular prisms and cubes

Lines, line segments, and rays

Difference between lines, line segments, and rays

Triangle angle example 1

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

Language and notation of basic geometry

Understanding basic ideas in geometry and how we represent them with symbols