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# Solution for If X = a ( T + 1 T ) and Y = a ( T − 1 T ) ,Prove that D Y D X = X Y ? - CBSE (Commerce) Class 12 - Mathematics

ConceptSimple Problems on Applications of Derivatives

#### Question

If  $x = a\left( t + \frac{1}{t} \right) \text{ and y } = a\left( t - \frac{1}{t} \right)$ ,prove that  $\frac{dy}{dx} = \frac{x}{y}$?

#### Solution

$\text{ We have, x } = a\left( t + \frac{1}{t} \right) \text{ and y } = a\left( t - \frac{1}{t} \right)$
$\Rightarrow \frac{dx}{dt} = a\frac{d}{dt}\left( t + \frac{1}{t} \right) \text{ and } \frac{dy}{dt} = a\frac{d}{dt}\left( t - \frac{1}{t} \right)$
$\Rightarrow \frac{dx}{dt} = a\left( 1 - \frac{1}{t^2} \right) \text{ and } \frac{dy}{dt} = a\left( 1 + \frac{1}{t^2} \right)$
$\Rightarrow \frac{dx}{dt} = a\left( \frac{t^2 - 1}{t^2} \right) \text{ and } \frac{dy}{dt} = a\left( \frac{t^2 + 1}{t^2} \right)$
$\therefore \frac{dy}{dx} = \frac{\frac{dy}{dt}}{\frac{dx}{dt}} = \frac{a\left( t^2 + 1 \right)}{t^2} \times \frac{t^2}{a\left( t^2 - 1 \right)}$
$\Rightarrow \frac{dy}{dx} = \frac{a\left( t^2 + 1 \right)}{t} \times \frac{t}{a\left( t^2 - 1 \right)}$
$\Rightarrow \frac{dy}{dx} = a\left( t + \frac{1}{t} \right) \times \frac{1}{a\left( t - \frac{1}{t} \right)}$
$\Rightarrow \frac{dy}{dx} = \frac{x}{y}$
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Solution If X = a ( T + 1 T ) and Y = a ( T − 1 T ) ,Prove that D Y D X = X Y ? Concept: Simple Problems on Applications of Derivatives.
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