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Geometry Difficulty 2.2 Junior Find the answer Canada

In the diagram, points $B$ , $C$ and $D$ lie on a line. Also, $\angle ABC = 90\degree$ and $\angle ACD = 150\degree$ .The value of $x$ is

Pick one

Solution

Solution 1

Since $\angle BCD$ is a straight angle, then $\$\angle$ ACB = $180\degree - \angle$
ACD = $180\degree - 150\degree = 30\degree$ . Since the measures of the angles in

Figure for this problem $\triangle$ ABC $add to$ $180\degree$ $, then$ $x\degree + 90\degree + 30\degree = 180\degree$ $and so$ x = 180 - 120 = 60$.

Solution 2

Since the measures of the angles in $\triangle ABC$ add to $180\degree$ , then $\angle ACB = 180\degree - \angle ABC - \angle BAC = 180\degree - 90\degree - x\degree = 90\degree - x\degree$ Since $\angle BCD = 180\degree$ , then $\begin{align*} \angle ACB + \angle ACD & = 180\degree \\ (90\degree - x\degree) + 150\degree & = 180\degree \\ 240 - x & = 180\end{align*}$ and so $x = 60$ .

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Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project.