Question

proof for sin(90+x)

Answer 1

sin(90+x)= sin90cosx + cos90sinx

Answer 2

\[\sin \left( x+y \right)=\sin x \cos y+\cos x \sin y\]

Answer 3

@narain: we don't "prove" sin (90+x ); we write out the expression using the sum identity for that expression. See surjithayer's identity, above. Please use that identity to simplify
sin (90+x).

Answer 4

sin (90 + x) = cos [90 - (90 + x)] = cos (-x) = cos x