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<p>will <a href="page.php?w=Superposition_principle">superpose</a> and add: the sum of the two waves is</p>

<p>Using the <a href="page.php?w=trigonometric_identity">trigonometric identity</a> for the sum of two cosines:  this can be written</p>

<p>This represents a wave at the original frequency, traveling to the right like its components, whose amplitude is proportional to the cosine of .<br/>
* Constructive interference: If the phase difference is an even multiple of :  then , so the sum of the two waves is a wave with twice the amplitude <br/>
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