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JEE Main 20246 AprilEvening Shift
Exam
JEE Main
Year
2024
Date
6 April
Shift
Evening Shift
Subject
Mathematics
Chapter
Hyperbola

JEE Main 2024 · 6 April · Evening Shift · Mathematics · Hyperbola

The length of the latus rectum and directrices of a hyperbola with...

The length of the latus rectum and directrices of a hyperbola with eccentricity e are 9 and x=±413x= \pm \frac{4}{\sqrt{13}}, respectively. Let the line y−3x+3=0y-\sqrt{3} x+\sqrt{3}=0 touch this hyperbola at \left(x_0, y_0\right).If. If\mathrm{m}istheproductofthefocaldistancesofthepoint(x0,y0)is the product of the focal distances of the point \left(x_0, y_0\right), then 4e2+m4 \mathrm{e}^2+\mathrm{m} is equal to ________

Correct answer

0

Step-by-step solution

Given 2 b2a=9\frac{2 \mathrm{~b}^2}{\mathrm{a}}=9 and ae=±43\frac{\mathrm{a}}{\mathrm{e}}= \pm \frac{4}{\sqrt{3}} equation of tangent y−3x+3=0y-\sqrt{3} x+\sqrt{3}=0 by equation of tangent Let slope =S=3=\mathrm{S}=\sqrt{3} Constant =−3=-\sqrt{3} By condition of tangency ⇒6=6a2−9a⇒a=2, b2=9\begin{aligned} & \Rightarrow 6=6 \mathrm{a}^2-9 \mathrm{a} \\ & \Rightarrow \mathrm{a}=2, \mathrm{~b}^2=9 \end{aligned}
Equation of Hyperbola is x24−y29=1\frac{x^2}{4}-\frac{y^2}{9}=1 and for tangent Point of contact is (4,33)=(x0,y0)(4,3 \sqrt{3})=\left(\mathrm{x}_0, \mathrm{y}_0\right)
Now e =1+94=132=\sqrt{1+\frac{9}{4}}=\frac{\sqrt{13}}{2} Again product of focal distances m=(x0e+a)(x0e−a)m+4e2=20e2−a2=20×134−4=61\begin{aligned} & \mathrm{m}=\left(\mathrm{x}_0 \mathrm{e}+\mathrm{a}\right)\left(\mathrm{x}_0 \mathrm{e}-\mathrm{a}\right) \\ & \mathrm{m}+4 \mathrm{e}^2=20 \mathrm{e}^2-\mathrm{a}^2 \\ & =20 \times \frac{13}{4}-4=61 \\ & \end{aligned}
(There is a printing mistake in the equation of directrix x=±43x= \pm \frac{4}{\sqrt{3}}. Corrected equation is x=±413x= \pm \frac{4}{\sqrt{13}} for directrix, as eccentricity must be greater than one, so question must be bonus)
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