To calculate the energy of a function, use the following equation.
$ E=\int_{t1}^{t2}{|f(t)|^2dt} $
For clarity, follow the example below.
$ E=\int_{0}^{2pi}{|2sin(t)|^2dt} $
$ E=\2 int_{0}^{2pi}{|sin(t)|^2dt} $
