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

Name all the regular polygons in diagram 16.

Name all the irregular polygons.

Diagram 17.

LESSON TWENTY-FIRST.

TRIANGLES.

ACUTE-ANGLED TRIANGLES.

In the triangle 1, what kind of an angle is b a c? a c b? c b a? (Diagram [17].)

Then it is called an acute-angled triangle.