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| − | <math> | + | <math>E = \int_{t_1}^{t_2} \! |f(t)|^2\ dt</math> |
| − | <math> | + | <math>=\int_0^{2\pi}{|2cos(t)|^2dt}</math> |
<math>=\int_0^{2\pi}{(2(2cos(t)^2-1)+2)dt}</math> | <math>=\int_0^{2\pi}{(2(2cos(t)^2-1)+2)dt}</math> | ||
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<math>=(4\pi)</math> | <math>=(4\pi)</math> | ||
</font> | </font> | ||
| − | |||
==Power== | ==Power== | ||
Revision as of 15:55, 3 September 2008
Signal
$ y(t)=2cos(t) $
Energy
According to formula of Energy of a singal,we can get:
$ E = \int_{t_1}^{t_2} \! |f(t)|^2\ dt $
$ =\int_0^{2\pi}{|2cos(t)|^2dt} $
$ =\int_0^{2\pi}{(2(2cos(t)^2-1)+2)dt} $
$ =\int_0^{2\pi}{2+cos(2t))dt} $
$ =(2t+sin(2t))|_{t=0}^{t=2\pi} $
$ =(4\pi+0-0-0) $
$ =(4\pi) $
Power
According to formula of Power of a singal,we can get: $ P = \frac{1}{2T}\int_{-T}^{T}\!|f(t)|^2\ dt $
$ = \frac{1}{4\pi}\int_{-2\pi}^{2\pi}\!|2\cos(t)|^2\ dt $
(comparing the integral part with Energy part, they are basically the same)
$ = \frac{1}{4\pi} $
$ = \frac{1}{4\pi}(4pi) $
$ = \pi $
