If cos theta= -sin theta, then sin^2 theta is?

a) 1/4
b) 1/2
c) sqrt2/2
d) - sqrt 2/2

please show me how you got the answer! thank you!

theta = -45 deg or 135 deg

sin theta = 1/sqrt 2 or -1/sqrt 2

sin^2 theta = 1/2 in either case