For a particular angle theta, the cosine function f(x) = a cos b(theta) has the following values within one cycle of the function. f(0) = 4; f(pi/4) = 0; f(pi/2) = -4; f(3pi/4) = 0; f(pi) = 4 what is the rule for the cosine function? a) y= 2 cos 4 theta b) y= 4 cos 2 theta c) y= -4 cos 3 theta d) y= 1/4cos 2 theta