Question

Answer the following questions in relation to the figure in Q.4.

(4) Write measures of the angles which form linear pairs with ∠AOD.

Answer 1

The sum of the measures of angles forming a linear pair is 180°.
Because $\angle AOC$ and $\angle AOD$ form a linear pair, $\angle AOC$ + $\angle AOD$ = 180°.
⇒ $\angle AOC$ + 120° = 180°
= $\angle AOC$ = 180° – 120°
= $\angle AOC$ = 60°

Also, $\angle BOD$ and $\angle AOD$ form a linear pair.
∴ $\angle BOD=60°$