All values of theta are positive. From left to right, the first peak occurs at (pi/2,1) and the second peak occurs at (9pi/2).

A. Write the graphs equation as a cosine function.
B. Write the graphs equation as a sine function.

1 answer

the period is 4?, so

f(x) = cos(x/2)
since cos(u)=1 at u=0, we have
f(x) = cos((x-?/2)/2)

see

http://www.wolframalpha.com/input/?i=cos((x-%CF%80%2F2)%2F2)+for+0+%3C%3D+x+%3C%3D+5pi

Now recall that cos(x) = sin(?/2 - u)