Question

cos^-1(-sqrt 2/2)

Answer 1

check your Unit Circle
if you don't have one -> http://i.stack.imgur.com/r8uHr.gif

Answer 2

cos^-1 (sqrt2/2) = inverse cos (sqrt2/2)

think of an angle which has a cosine equal to (sqrt2/2)

cos X = (sqrt2/2)

X = 45 degrees, also pi/4

surely, 45 degrees is between -90 and 180 degrees

hope that helped.

Answer 3

45