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Question
Evaluate the following:
sin 36° cos 9° + cos 36° sin 9°
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Solution
\[\sin36^\circ\cos9^\circ + \cos 36^\circ \sin9^\circ\]
\[ = \sin\left( 36^\circ + 9^\circ \right) \left[\text{ Using }\sin A \cos B + \cos A \sin B = \sin\left( A + B \right) \right]\]
\[ = \sin45^\circ = \frac{1}{\sqrt{2}}\]
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