Exercise 9 Page 348

Let's start by analyzing the given diagram. For the purposes of the solution, we will name the vertices of the triangles.

As we can see, ∠ 4 is an exterior angle of △ ABD. Because angles ∠ 1 and ∠ 2 do not share a vertex or corner of the triangle with ∠ 4, these are the corresponding remote interior angles. Let's now recall the Exterior Angle Inequality Theorem.

By this theorem, we can conclude that the measure of ∠ 4 is greater than the measures of ∠ 1 and ∠ 2. In other words, m∠ 1 and m ∠ 2 are less than m∠ 4.