Gujarati
10-2. Parabola, Ellipse, Hyperbola
normal

अतिपरवलय $\frac{x^2}{9}-\frac{y^2}{4}=1$, पर सरल रेखा $2 x-y=1$ के समान्तर स्पर्श रेखाये खींची गयी है। इन स्पर्श रेखाओं के अतिपरवलय पर स्पर्श बिन्दु (points of contacts) निम्न है

$(A)$ $\left(\frac{9}{2 \sqrt{2}}, \frac{1}{\sqrt{2}}\right)$

$(B)$ $\left(-\frac{9}{2 \sqrt{2}},-\frac{1}{\sqrt{2}}\right)$

$(C)$ $(3 \sqrt{3},-2 \sqrt{2})$

$(D)$ $(-3 \sqrt{3}, 2 \sqrt{2})$

A

$(B,D)$

B

$(B,C)$

C

$(A,D)$

D

$(A,B)$

(IIT-2012)

Solution

Slope of tangents $=2$

Equation of tangents $y=2 x \pm \sqrt{9.4-4}$

$\Rightarrow y=2 x \pm \sqrt{32} $

$\Rightarrow 2 x-y \pm 4 \sqrt{2}=0$

Let point of contact be $\left( x _1, y _1\right)$ then equation $(i)$ will be identical to the equation

$\frac{x x_1}{9}-\frac{y_1}{4}-1=0 $

$\therefore \frac{x_1 / 9}{2}=\frac{y_1 / 4}{1}=\frac{-1}{ \pm 4 \sqrt{2}} $

$\Rightarrow\left(x_1, y_1\right) \equiv\left(-\frac{9}{2 \sqrt{2}}, \frac{-1}{\sqrt{2}}\right) \text { and }\left(\frac{9}{2 \sqrt{2}}, \frac{1}{\sqrt{2}}\right)$

Standard 11
Mathematics

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