Exercise 19 Page 340

We want to find the missing angle of the given triangle. In order to do so, we will use the Triangle Exterior Angle Theorem. This theorem tells us that the measure of an exterior angle is equal to the sum of its two remote interior angles.

Now, let's apply this theorem to the given triangle.

The sum of m∠ 2 and 71^(∘) will give us the measure of the third angle, 92 ^(∘). m∠ 2 + 71=92 ⇒ m∠ 2=21