Question: If $ \sin ,(A-B)=\sin A,\cos B-\cos A,\sin B, $ then $ \sin 15{}^\circ $ will be
Options:
A) $ \frac{\sqrt{3}-1}{\sqrt{2}} $
B) $ \frac{\sqrt{3}}{2\sqrt{2}} $
C) $ \frac{\sqrt{3}+1}{2\sqrt{2}} $
D) $ \frac{\sqrt{3}-1}{2\sqrt{2}} $
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Answer:
Correct Answer: D
Solution:
- $ \sin 15{}^\circ =\sin ,(45{}^\circ -30{}^\circ ) $
$ =\sin 45{}^\circ \cdot \cos 30{}^\circ -\cos 45{}^\circ \cdot \sin 30{}^\circ $
$ =\frac{1}{\sqrt{2}}\times \frac{\sqrt{3}}{2}-\frac{1}{\sqrt{2}}\times \frac{1}{2} $
$ =\frac{\sqrt{3}}{2\sqrt{2}}-\frac{1}{2\sqrt{2}}=\frac{\sqrt{3}-1}{2\sqrt{2}} $