If the tangent to the curve $y=\frac{x}{x^2-3}, x \in R,(x \neq \pm \sqrt{3})$ at a point $(\alpha, \beta)…

If the tangent to the curve $y=\frac{x}{x^2-3}, x \in R,(x \neq \pm \sqrt{3})$ at a point $(\alpha, \beta) \neq(0,0)$ on it, is parallel to the line $2 x+6 y-11=0$, then
  1. $|2 \alpha+6 \beta|=11$
  2. $|6 \alpha+2 \beta|=9$
  3. $|6 \alpha+2 \beta|=19$
  4. $|2 \alpha+6 \beta|=19$

Solution

$y=\frac{x}{x^2-3} \Rightarrow \frac{d y}{d x}=\frac{-\left(3+x^2\right)}{\left(x^2-3\right)^2}$ Now slope of $2 x+6 y-11=0$ is $\frac{-1}{3}$ $\begin{aligned} & \frac{\mathrm{A}}{\mathrm{Q}}-\frac{1}{3}=\frac{-\left(3+x^2\right)}{\left(x^2-3\right)^2} \\ & \Rightarrow x^4-9 x^2=0 \\ & \Rightarrow x^2\left(x^2-9\right)=0 \\ & \Rightarrow x=0 \text { or } x= \pm 3\end{aligned}$ But $x \neq 0$ so $x= \pm 3 \Rightarrow y= \pm \frac{1}{2}$ Hence, $\alpha= \pm 3, \beta= \pm \frac{1}{2}$ $\Rightarrow|6 \alpha+2 \beta|=\left| \pm\left(6 \times 3+2 \times \frac{1}{2}\right)\right|=19$

Asked in: MHT CET 2022 (06 Aug Shift 1)

Practice more Applications of Derivatives questions on Aicharya