Answer:
see explanation
Step-by-step explanation:
Using the cosine addition identity
cos(x + y) = cosxcosy - sinxsiny
and cos([tex]\frac{\pi }{2}[/tex]) = 0, sin([tex]\frac{\pi }{2}[/tex]) = 1
cos(x + [tex]\frac{\pi }{2}[/tex])
= cosxcos([tex]\frac{\pi }{2}[/tex]) - sinxsin([tex]\frac{\pi }{2}[/tex])
= cosx × 0 - sinx × 1
= 0 - sinx
= - sinx
