The curves $\frac{x^2}{a^2}+\frac{y^2}{4}=1$ and $y^3=16 x$ intersect each other orthogonally, then…

The curves $\frac{x^2}{a^2}+\frac{y^2}{4}=1$ and $y^3=16 x$ intersect each other orthogonally, then $\mathrm{a}^2=$
  1. 2
  2. $\frac{3}{4}$
  3. $\frac{1}{2}$
  4. $\frac{4}{3}$

Solution

$\begin{aligned} & \frac{x^2}{a^2}+\frac{y^2}{4}=1 \\ & \therefore \frac{1}{a^2} 2 x+\frac{1}{4} 2 y \frac{d y}{d x}=0 \quad \Rightarrow \frac{d y}{d x}=\left(\frac{-x}{a^2}\right)\left(\frac{4}{y}\right) \end{aligned}$ Also $\mathrm{y}^3=16 \mathrm{x}$ $\therefore 3 y^2 \frac{d y}{d x}=16 \Rightarrow \frac{d y}{d x}=\frac{16}{3 y^2}$ Since curves intersect orthogonally, from (1) and (2), we write $\left(\frac{-x}{a^2}\right)\left(\frac{4}{y}\right)\left(\frac{16}{3 y^2}\right)=-1$ $\therefore \frac{64 x}{3 a^2 y^3}=1$ and we have $y^3=16 x$ $\therefore \frac{64 \mathrm{x}}{3 \mathrm{a}^2(16 \mathrm{x})}=1 \Rightarrow \mathrm{a}^2=\frac{4}{3}$

Asked in: MHT CET 2021 (21 Sep Shift 1)

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