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JEE Main 202224 JuneMorning Shift
Exam
JEE Main
Year
2022
Date
24 June
Shift
Morning Shift
Subject
Mathematics
Chapter
Parabola

JEE Main 2022 · 24 June · Morning Shift · Mathematics · Parabola

If two tangents drawn from a point (α, β) lying on the ellipse 25 x...

If two tangents drawn from a point (α,β)\left(\alpha, \beta\right) lying on the ellipse 25x2+4y2=125{x}^{2} + 4{y}^{2} = 1 to the parabola y2=4x{y}^{2} = 4x are such that the slope of one tangent is four times the other, then the value of (10α+5){\left(10\alpha + 5\right)}^{2} + {\left(16{\beta}^{2} + 50\right)}^{2} equals ______

Correct answer

0

Step-by-step solution

Let α=15cosθ,β=12sinθ\alpha = \dfrac{1}{5}cos\theta, \beta = \dfrac{1}{2}sin\theta

Equation of tangent to y2=4x{y}^{2} = 4x with slope mm will be y=mx+1my = mx + \dfrac{1}{m}

Since the tangent passes through \left(\alpha, \beta\right),so</p><p>, so</p><p>\dfrac{1}{2}sin\theta = \dfrac{m}{5}cos\theta + \dfrac{1}{m}</p><p></p><p>⇒ {m}^{2}\left(\dfrac{cos\theta}{5}\right) - m\left(\dfrac{1}{2}sin\theta\right) + 1 = 0</p><p>Asitisaquadraticequationin</p><p>As it is a quadratic equation inmsoitwillhavetworootsso it will have two roots{m}_{1} and {m}_{2}</p><p>Given</p><p>Given{m}_{1} = 4{m}_{2}</p><p>Now,</p><p>Now,{m}_{1} + {m}_{2} = \dfrac{\dfrac{1}{2}sin\theta}{\dfrac{cos\theta}{5}}</p><p></p><p>{m}_{1}{m}_{2} = \dfrac{5}{cos\theta}</p><p>Aftereliminating</p><p>After eliminating{m}_{1} and {m}_{2},weget,</p><p>, we get,</p><p>cos\theta = \dfrac{- 5 \pm \sqrt{29}}{2} ⇒ \cos^{2}\theta = \dfrac{54 \pm 10\sqrt{29}}{4}</p><p>i.e.</p><p>i.e.\alpha = \dfrac{- 5 \pm \sqrt{29}}{10} ⇒ 10\alpha + 5 = \pm \sqrt{29}</p><p>and</p><p>and{\beta}^{2} = \dfrac{1}{4}\sin^{2}\theta ⇒ 16{\beta}^{2} = - 50 \pm 10\sqrt{29}</p><p>Hence,</p><p>Hence,{\left(10\alpha + 5\right)}^{2} + {\left(16{\beta}^{2} + 50\right)}^{2} = 2929$

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