Khan Academy
Khan Academy: Classifying Shapes by Line and Angle Types
Explains how to classify 2D shapes based on the properties of their sides and angles. [2:15]
Khan Academy
Khan Academy: Classifying Quadrilaterals
Demonstrates how to decide which quadrilaterals match a set of given properties. [2:28]
Khan Academy
Khan Academy: Composing Shapes
Shows how shapes can be put together to make new shapes. [2:04]
Sophia Learning
Sophia: Regular Polygon Diagonals Practice
The instructor of this video lesson demonstrates how to find the number of diagonals in a regular polygon using a formula. [3:01]