I just want to make sure I am doing this right.

Find the average value of the function n the given interval

f(x)=sec^2 (x/2) [0, pi/2]

So I integrated from 0 to pi/2. but I am stuck on what the anti derivative of sec^2 (x/2) is... I know the anti derivative of sec^2 (x) is tan (x)...

Thanks