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The value of sin 15° sin 30° sin 75° is:
Question

The value of sin 15° sin 30° sin 75° is:

A.

122\frac{1}{2\sqrt2}​​

B.

18\frac{1}{8}​​

C.

32\frac{3}{2}​​

D.

14\frac{1}{4}​​

Correct option is B

Given:

sin15sin30sin75\sin 15^\circ \cdot \sin 30^\circ \cdot \sin 75^\circ​​

Formula Used:

sin15=624,sin30=12,sin75=6+24\sin 15^\circ = \frac{\sqrt{6} - \sqrt{2}}{4}, \quad \sin 30^\circ = \frac{1}{2}, \quad \sin 75^\circ = \frac{\sqrt{6} + \sqrt{2}}{4}​​

Solution:

sin15sin30sin75=(624)×(12)×(6+24)\sin 15^\circ \cdot \sin 30^\circ \cdot \sin 75^\circ = \left( \frac{\sqrt{6} - \sqrt{2}}{4} \right) \times \left( \frac{1}{2} \right) \times \left( \frac{\sqrt{6} + \sqrt{2}}{4} \right)​​

So,

12×(62)(6+2)16=12×416=18\frac{1}{2} \times \frac{(\sqrt{6} - \sqrt{2})(\sqrt{6} + \sqrt{2}) }{16} = \frac{1}{2} \times \frac{4}{16} = \frac{1}{8}

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