Question

plzz help me very urgent prove that​

Answer 1

Answer:

formula used here,

$\sin( \alpha ) + \sin( \beta ) = 2 \sin( \frac{ \alpha + \beta }{2} ) \cos( \frac{ \alpha - \beta }{2} ) \\ \cos( \alpha ) - \cos( \beta ) = 2 \sin( \frac{ \alpha + \beta }{2} ) \sin( \frac{ \beta - \alpha }{2} ) \\ \cos( - \alpha ) = \cos( \alpha )$