Question

Find the value of an $\angle ABC.$

• A. ${100}^o$
• B. ${80}^o$
• C. ${40}^o$
• D. ${140}^o$

Answer 1

The correct option is C ${40}^o$

The angle in the semicircle theorem tells us that $\angle ACB={90}^o$.
Now, use angle sum property of a triangle to find $\angle ABC$:
$\angle ABC+{50}^o+{90}^o={180}^o$
$\angle ABC={40}^o$