Chapter 9.4, Problem 5WE

To determine

To find $m\left(BC\right)$

Answer to Problem 5WE

$m\left(BC\right)={80}^{\circ }$

Explanation of Solution

Given information :

Following diagram provided

$O$ is the centre of the circle.

Since $m\left(AD\right)={360}^{\circ }-{120}^{\circ }$

$\Rightarrow m\left(AD\right)={240}^{\circ }$

Since $\Rightarrow \overline{AB}=\overline{BC}=\overline{CD}$

So, we have divide ${240}^{\circ }$ into three equal parts.

Thus, $m\left(BC\right)=\frac{{240}^{\circ }}{3}$

$\therefore m\left(BC\right)={80}^{\circ }$