Question

$\cos c+\cos d$ is equal to

Answer 1

Determine $\cos c+\cos d$ formula

From the trigonometric identity,

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

Hence, $\cos c+\cos d$ is equal to $2\cos \left(\frac{c+d}{2}\right)\cos \left(\frac{c-d}{2}\right)$.