If $\sqrt{x}+\sqrt{y}=\sqrt{x y}$, then $\frac{d y}{d x}=$

If $\sqrt{x}+\sqrt{y}=\sqrt{x y}$, then $\frac{d y}{d x}=$
  1. $-\left(\frac{y}{x}\right)^{\frac{3}{2}}$
  2. $\left(\frac{x}{y}\right)^{\frac{3}{2}}$
  3. $-\left(\frac{x}{y}\right)^{\frac{3}{2}}$
  4. $\left(\frac{y}{x}\right)^{\frac{3}{2}}$

Solution

We have $\sqrt{x}+\sqrt{y}=\sqrt{x y}$ Dividing both sides by $\sqrt{x y}$, we get $\frac{1}{\sqrt{y}}+\frac{1}{\sqrt{x}}=1$ Differentiating both sides w.r.t. $x$, we get $\begin{aligned} &\left(\frac{-1}{2}\right)\left(\frac{1}{y^{3 / 2}}\right)\left(\frac{d y}{d x}\right)-\left(\frac{1}{2}\right)\left(\frac{1}{x^{3 / 2}}\right)=0 \\ \therefore & \frac{d y}{d x}=-\left(\frac{y}{x}\right)^{3 / 2} \end{aligned}$

Asked in: MHT CET 2020 (12 Oct Shift 2)

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