Marks' first lessons in geometry / In two parts. Objectively presented, and designed for the use of primary classes in grammar schools, academies, etc.

by Bernhard Marks

Read the interior angles between the parallel lines g h and k l.

Why is o p l an interior angle?

What is an interior angle?

EXTERIOR ANGLES.

Is the angle a m e between the parallels, or outside of them?

It is called an exterior angle.

Read three other exterior angles formed by the lines a b, c d, and e f.

Why is the angle c n f an exterior angle?

An exterior angle is one that lies outside of the parallels.