waecmaths question:
If $\sin 3y=\cos 2y$ and ${{0}^{\circ }}\le y\le {{90}^{\circ }}$, find the value of y
Option A:
18o
Option B:
36o
Option C:
54o
Option D:
90o
waecmaths solution:
$\begin{align} & sin\theta =cos(90-\theta ) \\ & \sin 3y=\cos (90-3y)=\cos 2y \\ & \cos (90-3y)=\cos 2y \\ & 90-3y=2y \\ & 5y=90 \\ & y={{18}^{\circ }} \end{align}$
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