For a particular angle theta, the cosine function f(x)=a cos b(theta) has the following values with in 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 4theta b. y=4 cos 2theta c. y=-4 cos 3theta d. y= 1/4 cos 2theta