Math Planet
Math Planet: Pre Algebra: Angles and Parallel Lines
Explains angles and parallel lines through examples and a video lesson.
University of Georgia
University of Georgia: Inter Math: Exterior Angles
Intermath Dictionary's site defines terms relating to angles, gives examples, and offers interactive exercises.
Math Open Reference
Math Open Reference: Areas by Slicing
Learn about alternate exterior angles with this handy reference guide. Provides a detailed definition and examples that enhance further explanation. Includes links to related topics.
Illustrative Mathematics
Illustrative Mathematics: G Gpe.5 Triangles Inscribed in Circle
In this task, students use ideas about linear functions to determine when certain angles are right angles. They use the fact that two lines (if not vertical or horizontal) are perpendicular when their slopes are inverse reciprocals, as...