This problem anticipates a major result derived in the next section. Show that the sum of the measures of the interior angles of any triangle is 180°.

a. Draw three triangles, one with all acute angles, one with a right angle, and a third with an obtuse angle. A triangle with all acute angles is shown here:

b. Tear apart the angles of each triangle you’ve drawn, and place them together to form a straight angle at the bottom, as shown here: