Chapter 1.4, Problem 7PSA

To determine

To Prove : $\angle XYZ\text{ is a right angle}\text{.}$

Explanation of Solution

Given information :

  $\begin{array}{l}\angle 1=20°\\ \angle 2=40°\\ \angle 3=30°\end{array}$

  

Proof:

Here, we have

  $\begin{array}{l}\angle XYZ=\angle 1+\angle 2+\angle 3=20°+40°+30°=90°\\ \Rightarrow \angle XYZ=90°\end{array}$

  $\text{Thus,}\angle XYZ\text{ is a right angle}\text{.}$