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<p>the <a href="page.php?w=Energy_%28signal_processing%29">energy</a> of a signal  is given by</p>

<p>Assuming the total energy is finite (i.e.  is a <a href="page.php?w=square-integrable_function">square-integrable function</a>) allows applying <a href="page.php?w=Parseval%27s_theorem">Parseval's theorem</a> (or <a href="page.php?w=Plancherel%27s_theorem">Plancherel's theorem</a>). That is,</p>

<p>where</p>

<p>is the <a href="page.php?w=Fourier_transform">Fourier transform</a> of  at <a href="page.php?w=frequency">frequency</a>  (in <a href="page.php?w=Hz">Hz</a>).</p><p>
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