Enquiry For Math

May i know how to solve this eqn?
Finding energy signal of a periodic signal
Ex= integrate from infinity to -infinity (Acos(2 pi fo t))^2 dt?
Any one can help me?

The integral of:

A*Cos(2*PI*t)^2 with respect to "t" from -inf to +inf is:


/inf
|
| A cos(2 pi t)^2 dt = Infinity
/-inf


The integral

/
| 2
| A cos(2 pi t) dt
|
/

has a solution


[ A( 1/2cos(2 pi t) sin(2 pi t) + pi t) ] / 2*pi + C

I can't remember exactly the forumla to calculate the enrergy of a periodic signal nor can i find it on the web, but if it is simply the integral of your signal from neg. inf. to inf., then your energy will be infinite. Since your signal is a sinusoid squared, when you integrate something that's all-positive and periodic from neg. inf. to inf., you get infinity as your answer. As for the math, use the double-angle formula (cos^2(x) = 1/2 + cos(2x)/2 ) to simplify that integral; you shouldn't have a problem from there.