Question

plz answer fast......: )

Answer 1

You are likely to be familiar with the identity
$\cos( \alpha ) + \cos( \beta ) = 2 \cos( \frac{ \alpha + \beta }{2} ) \cos( \frac{ \alpha - \beta }{2} )$
and the fact that
$\cos( - \alpha ) = \cos( \alpha )$
Thank me later!!

Answer 2

the above ans is coreect