Math Planet
Math Planet: Pre Algebra: Angles and Parallel Lines
Explains angles and parallel lines through examples and a video lesson.
Homeschool Math
Homeschool Math: Parallel and Perpendicular Lines
This lesson explains what are parallel and perpendicular lines and includes varied exercises and a video that shows how to draw a perpendicular line and a rectangle using a protractor or a triangular ruler.
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...