A) \[2\cos \left[ \frac{C+D}{2} \right]\cos \left[ \frac{C-D}{2} \right]\]
B) \[2\sin \left[ \frac{C+D}{2} \right]\sin \left[ \frac{C-D}{2} \right]\]
C) \[2\cos \left[ \frac{C+D}{2} \right]\sin \left[ \frac{C-D}{2} \right]\]
D) \[2\sin \left[ \frac{C+D}{2} \right]\cos \left[ \frac{C-D}{2} \right]\]
Correct Answer: A
Solution :
\[\cos C+\cos D\] \[=2\cos \frac{C+D}{2}.\cos \frac{C-D}{2}\]
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