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Question: Answered & Verified by Expert
If $\sin 2 \theta=\cos 3 \theta$, where $0 < \theta < \frac{\pi}{2}$, then what is $\sin \theta$ equal
to ?
MathematicsTrigonometric Ratios & IdentitiesNDANDA 2019 (Phase 1)
Options:
  • A $\frac{\sqrt{5}+1}{4}$
  • B $\frac{\sqrt{5}-1}{4}$
  • C $\frac{\sqrt{5}+1}{16}$
  • D $\frac{\sqrt{5}-1}{16}$
Solution:
1136 Upvotes Verified Answer
The correct answer is: $\frac{\sqrt{5}-1}{4}$
$\begin{aligned} \sin 2 \theta=\cos 3 \theta \\ \Rightarrow \sin 2 \theta=\sin \left(90^{\circ}-3 \theta\right) \\ 2 \theta=90^{\circ}-3 \theta \quad \therefore \sin \theta=\sin 18^{\circ}=\frac{\sqrt{5}-1}{4} \\ & \Rightarrow 5 \theta=90^{\circ} \\ & \Rightarrow \theta=18^{\circ} \\ & \Rightarrow\left(\frac{1}{q}\right)(p)=1 \end{aligned}$
$\Rightarrow \mathrm{p}=\mathrm{q}$

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