I am having problems with this and was hoping somebody could assist. The polar function to integrate is:

cos^2 7t

cos^2 7t = 1/2(1+cos 14t)

1/4|(1+cos 14t)^2 dt

=1/4|1+2cos 14t+cos^2 14t dt

=1/4|1dt + 1/2|cos 14t dt + 1/8|1dt + 1/8|cos 28t dt

After evaluating this I get :-

3t/8+(8sin 14t+sin 28t)/224 +C.

However the answer given is:-

t/2+(sin 14t)/28 + C