The value of $\sin ^{2}\left(\frac{\pi}{8}\right)=$

The value of $\sin ^{2}\left(\frac{\pi}{8}\right)=$
  1. $\frac{\sqrt{2}+1}{2 \sqrt{2}}$
  2. $\frac{\sqrt{5}+1}{2 \sqrt{2}}$
  3. $\frac{\sqrt{5}-1}{2 \sqrt{2}}$
  4. $\frac{\sqrt{2}-1}{2 \sqrt{2}}$

Solution

$\begin{aligned} \sin ^{2}\left(\frac{\pi}{8}\right) &=\frac{1-\cos 2\left(\frac{\pi}{8}\right)}{2} \\ &=\frac{1-\cos \frac{\pi}{4}}{2}=\frac{1-\frac{1}{\sqrt{2}}}{2}=\frac{\sqrt{2}-1}{2 \sqrt{2}} \end{aligned}$

Asked in: MHT CET 2020 (20 Oct Shift 2)

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