Remember year 9 math. ASTC
d) -cos (7pi/8) = cos(pi/8) . Now use the the theorem f^-1(f(x)) = x to get pi/8.
f) I presume can figure out the value -2sin(4pi/3). Now if you know the exact value of tan^-1(sqrt(3)) you will get the answer. Remember the special triangles i.e. {1, 1, sqrt(2)} and...