Question

If cosC + cosD = x, then value of x is

A) 2cos[(C+D)/2]cos[(C-D)/2] B) 2sin[(C+D)/2]sin[(C-D)/2] C) 2cos[(C+D)/2]sin[(C-D)/2] D) 2sin[(C+D)/2]cos[(C-D)/2]

Answer 1

Answer:

Option A

Step-by-step explanation:

$cos c + cos d \: = \: 2 \cos( \frac{c + d}{2\\ } ) \cos( \frac{c - d}{2} )$

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