# Why does the given solution we dont have to integrate the rect function?

In the given solution energy is given as

$$E=\dfrac{A^2}{2}\int_{-0.5T}^{0.5T}1+\cos\left(\dfrac{2\pi t}{T}\right)dt=\dfrac{1}{2}A^2T$$

Why does the rect function disappear?

• Please change your image. It is very small and it is impossible to understand what does it mean. – SergV Oct 1 '15 at 11:07

It is implicit in the integral. You compute it just from $-0.5T$ to $+0.5T$, where the $\mbox{rect}$ is constant and equal to 1.