The value of \(\left(\sin 210^{\circ}\right)\left(\sin 585^{\circ}\right)\) is

The value of \(\left(\sin 210^{\circ}\right)\left(\sin 585^{\circ}\right)\) is
  1. \(\frac{1}{2 \sqrt{2}}\)
  2. \(\frac{-1}{2 \sqrt{2}}\)
  3. \(\frac{1}{\sqrt{3}}\)
  4. \(\frac{-1}{\sqrt{3}}\)

Solution

\(\begin{aligned} \sin 210^{\circ} \cdot \sin 585^{\circ} & =\sin \left(180^{\circ}+30^{\circ}\right) \cdot \sin \left(540^{\circ}+45^{\circ}\right) \\ & =-\sin 30^{\circ}\left(-\sin 45^{\circ}\right) \\ & =\frac{-1}{2} \times \frac{-1}{\sqrt{2}}=\frac{1}{2 \sqrt{2}} \end{aligned}\) Hence, option (a) is correct.

Asked in: AP EAMCET 2020 (18 Sep Shift 2)

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