precalculus
posted by ama .
write each expression as the sine, cosine or tangent of a double angle. then find the exact value of the expression.
a. 2sin 22.5 cos 22.5
b. cos^2 105 sin^2 105

a, use
sin 45 = cos 45 = 1/sqrt 2
b, use
105 = (1/2) 210 which is 180 + 30
so use
sin 210 = 1/2
cos 210 = sqrt 3/2