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Let $$\mathrm{P}\left(x_{0}, y_{0}\right)$$ be the point on the hyperbola $$3 x^{2}-4 y^{2}=36$$, which is nearest to the line $$3 x+2 y=1$$. Then $$\sqrt{2}\left(y_{0}-x_{0}\right)$$ is equal to :

JEE · Math · previous-year question

  1. A.3
  2. B.$$-$$9correct
  3. C.$$-$$3
  4. D.9

Answer

B. $$-$$9

Explanation

If $\left(x_0, y_0\right)$ is point on hyperbola then tangent at $\left(x_0, y_0\right)$ is parallel to $3 x+2 y=1$ Equation of tangent $= \frac{x x_0}{12}-\frac{y y_0}{9}=2$ Slope of tangent $=\frac{-3}{2}$ Equation of tangent in slope form $y=\frac{-3}{2} x \pm \sqrt{12 \cdot \frac{9}{4}-9}$ $y=\frac{-3}{2} x \pm 3 \sqrt{2}$ or $3 x+2 y=6 \sqrt{2}$ Comparing $$ \begin{aligned} & \frac{\frac{x_0}{12}}{3}=\frac{\frac{-y_0}{9}}{2}=\frac{1}{6 \sqrt{2}} \\\\ & x_0=3 \sqrt{2}, y_0=\frac{-3}{\sqrt{2}} \\\\ & \sqrt{2}\left(y_0-x_0\right)=-3-6=-9 \\\\ & \end{aligned} $$

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