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JEE Main 202431 JanuaryEvening Shift
Exam
JEE Main
Year
2024
Date
31 January
Shift
Evening Shift
Subject
Mathematics
Chapter
Ellipse

JEE Main 2024 · 31 January · Evening Shift · Mathematics · Ellipse

Let P be a parabola with vertex (2, 3) and directrix 2x + y = 6 ....

Let PP be a parabola with vertex (2,3)\left(2, 3\right) and directrix 2x+y=62x + y = 6. Let an ellipse E:x2a2+y2b2=1,a>bE: \dfrac{{x}^{2}}{{a}^{2}} + \dfrac{{y}^{2}}{{b}^{2}} = 1, a > b of eccentricity 12\dfrac{1}{\sqrt{2}} pass through the focus of the parabola PP. Then the square of the length of the latus rectum of EE, isLet P be a parabola with vertex (2, 3) and directrix 2x + y = 6 . Let an ellipse E: x ^ 2 a ^ 2 + y ^ 2 b ^ 2 = 1, a >

Options

  1. A3858\dfrac{385}{8}
  2. B3478\dfrac{347}{8}
  3. C51225\dfrac{512}{25}
  4. D65625\dfrac{656}{25}

Correct answer

D. 65625\dfrac{656}{25}

Step-by-step solution

Let P be a parabola with vertex (2, 3) and directrix 2x + y = 6 . Let an ellipse E: x ^ 2 a ^ 2 + y ^ 2 b ^ 2 = 1, a >

Let ZZ be the foot of perpendicular from vertex to directrix of parabola,

Now, finding ZZ we get,

⇒x−22=y−31=−(4+3)−64+1⇒ \dfrac{x - 2}{2} = \dfrac{y - 3}{1} = - \dfrac{\left(4 + 3\right) - 6}{4 + 1}

⇒x−22=y−31=−15⇒ \dfrac{x - 2}{2} = \dfrac{y - 3}{1} = \dfrac{- 1}{5}

⇒x−22=−15,y−31=−15⇒ \dfrac{x - 2}{2} = \dfrac{- 1}{5}, \dfrac{y - 3}{1} = \dfrac{- 1}{5}

⇒x=125,y=165⇒ x = \dfrac{12}{5}, y = \dfrac{16}{5}

⇒Z≡(125,165)⇒ Z ≡ \left(\dfrac{12}{5}, \dfrac{16}{5}\right)

Eccentricity of ellipse is given as 12\dfrac{1}{\sqrt{2}}.

Now, finding b2{b}^{2} using eccentricity formula we get,

⇒b2=a2(1−e2)=a22⇒ {b}^{2} = {a}^{2}\left(1 - {e}^{2}\right) = \dfrac{{a}^{2}}{2}

So, equation of ellipse will be,

⇒14425a2+25625×a22=1⇒ \dfrac{144}{25{a}^{2}} + \dfrac{256}{25 \times \dfrac{{a}^{2}}{2}} = 1 {as (x,y)≡\left(x, y\right) ≡\left(\dfrac{12}{5}, \dfrac{16}{5}\right)}</p><p>⇒ \dfrac{144}{25{a}^{2}} + \dfrac{512}{25{a}^{2}} = 1</p><p></p><p>⇒ \dfrac{656}{25{a}^{2}} = 1</p><p></p><p>⇒ {a}^{2} = \dfrac{656}{25}</p><p></p><p>⇒ {b}^{2} = \dfrac{328}{25}</p><p>Lengthoflatusrectumisgivenby,<br/></p><p>Length of latus rectum is given by,<br/>L = \dfrac{2{b}^{2}}{a}.</p><p>.</p><p>⇒ L = \dfrac{2 \times \dfrac{328}{25}}{\dfrac{\sqrt{656}}{5}}</p><p></p><p>⇒ L = \dfrac{\sqrt{656}}{5}</p><p></p><p>⇒ {L}^{2} = \dfrac{656}{25}

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