Explanation and example of angles around a point.
Math is Fun

This page goes through the definitions and then some practice problems for identifying them
Homeschool Math

A site that goes through general descriptions of angles and the types of angles, but includes additional interactive construction demonstrations.
Hamilton's Math to Build On!

Basic overview of supplementary angles
Math is Fun

Definition of an acute angle (one less than 90 degrees).
Math Open Reference

Definition of 'altitude' and the various different ways the word is used in geometry
Math Open Reference

Gives examples of problems with intercepted arc, central angle, and angles inside and outside the circle.
Online Math Learning

Identify the missing angle measurement in each set of supplementary angles. Answers included.
MathDrills.com

Explanation of acute angles
Math is Fun

Identify the missing angle measurement in each set of complementary angles. Answers included.
MathDrills.com
