Question

If
${ \cos(\frac{ {x}^{2} - {y}^{2} }{ {x}^{2} + {y}^{2} } ) }^{ - 1} = 2k$
Show That
$y \frac{dy}{dx} = x { \tan(k) }^{2}$
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Answer 1

Step-by-step explanation:

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