If siny=cosx, then find dy/dx at the point (pi/2, pi)

Question

A. -1
B. 0
C. 1
D. pi/2
E. None of these

I got C

Answer 1

siny = cosx
cosy y' = -sinx
-y' = -1
C is correct

Answer 2

-1
Siny=cosx
Y=sin'cosx
Y=sin'sinpi/2-x
Y=pi/2-x
Y'=0-1=-1