$ E_\infty = \frac{1}{t_2-t_1}\int_{t_1}^{t_2}[x(t)]^2 dt $
ex: $ E_\infty = \int_{-\infty}^{\infty} [x(t)]^2 dt $
$ P_\infty lim N-> - \infty = \frac{1}{2*N+1}\int_{-N}^{N}[x(t)]^2 dt $
