Given a signal $$x(t)=16\cos(20\pi t+\frac\pi 4)+6\cos(30\pi t+\frac\pi 6)+4\cos(40\pi t+\frac\pi 3)$$how can I calculate the power contained in a frequency interval, say 12Hz to 22Hz. The total power is $\frac{16^2}{2}+\frac{6^2}{2}+\frac{4^2}{2}=154$

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    $\begingroup$ Determine the frequencies of the three sinusoids and then just count the ones inside the given interval. $\endgroup$ – Matt L. Aug 9 '14 at 18:22
  • $\begingroup$ thanks,I got it. It is the power of last two cos terms. 18+8=26W $\endgroup$ – mahes Aug 9 '14 at 18:46

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