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JEE Main 202313 AprilMorning Shift
Exam
JEE Main
Year
2023
Date
13 April
Shift
Morning Shift
Subject
Mathematics
Chapter
Ellipse

JEE Main 2023 · 13 April · Morning Shift · Mathematics · Ellipse

Let the tangent and normal at the point (3 3 , 1) on the ellipse x...

Let the tangent and normal at the point (33,1)\left(3\sqrt{3}, 1\right) on the ellipse x236+y24=1\dfrac{{x}^{2}}{36} + \dfrac{{y}^{2}}{4} = 1 meet the y−y -axis at the points AandBA and B respectively. Let the circle CC be drawn taking ABAB as a diameter and the line x=25x = 2\sqrt{5} intersect CC at the points PandQ.P and Q . If the tangents at the points PandQP and Q on the circle intersect at the point (α,β),\left(\alpha, \beta\right), then α2−β2{\alpha}^{2} - {\beta}^{2} is equal to

Options

  1. A6161
  2. B6060
  3. C3045\dfrac{304}{5}
  4. D3145\dfrac{314}{5}

Correct answer

C. 3045\dfrac{304}{5}

Step-by-step solution

Given that x236+y24=1\dfrac{{x}^{2}}{36} + \dfrac{{y}^{2}}{4} = 1

Observe that \left(3\sqrt{3}, 1\right)liesonthegivenellipse.</p><p>Equationoftangenttotheellipseatthegivenpointislies on the given ellipse.</p><p>Equation of tangent to the ellipse at the given point isT: \dfrac{3\sqrt{3}x}{36} + \dfrac{y}{4} = 1</p><p></p><p>⇒ \dfrac{\sqrt{3}x}{12} + \dfrac{y}{4} = 1</p><p>Equationofnormalpassingthroughsamepointwillbe</p><p>Equation of normal passing through same point will beN: \dfrac{x - 3\sqrt{3}}{\dfrac{3\sqrt{3}}{36}} = \dfrac{y - 1}{\dfrac{1}{4}}</p><p></p><p>⇒ \dfrac{12x - 36\sqrt{3}}{\sqrt{3}} = 4y - 4</p><p></p><p>⇒ 3x - 9\sqrt{3} = \sqrt{3}y - \sqrt{3}</p><p></p><p>⇒ 3x - \sqrt{3}y = 8\sqrt{3}</p><p>Nowtangentandnormalintersectsthe</p><p>Now tangent and normal intersects they -axisataxis atAandandBrespectively.</p><p>respectively.</p><p>A\left(0, 4\right)B\left(0, - 8\right)</p><p>Equationofcirclewith</p><p>Equation of circle withABasdiameterwillbe</p><p>(x−x1)(x−x2)+(y−y1)(y−y2)=0as diameter will be</p><p>\left(x - {x}_{1}\right)\left(x - {x}_{2}\right) + \left(y - {y}_{1}\right)\left(y - {y}_{2}\right) = 0

⇒x2+(y−4)(y+8)=0\text{⇒}{x}^{2} + ( y - 4 ) ( y + 8 ) = 0

Line x=25x = 2\sqrt{5} intersects the circle.

⇒20+y2+4y−32=0⇒ 20 + {y}^{2} + 4y - 32 = 0

⇒y2+4y−12=0⇒ {y}^{2} + 4y - 12 = 0

⇒(y+6)(y−2)=0⇒ ( y + 6 ) ( y - 2 ) = 0

Hence P(25,−6)Q(25,2)P ( 2\sqrt{5}, - 6 ) Q ( 2\sqrt{5}, 2 )

Now let us find the equation of tangents to the circle at P,QP, Q.

⇒T:xx1+yy1+2y+2y1−32=0⇒ T: x{x}_{1} + y{y}_{1} + 2y + 2{y}_{1} - 32 = 0

⇒T1:25x−6y+2y−12−32=0⇒ {T}_{1}: 2\sqrt{5}x - 6y + 2y - 12 - 32 = 0

⇒25x−4y=44⇒ 2\sqrt{5}x - 4y = 44

⇒T1:5x−2y=22........(i)⇒ {T}_{1}: \sqrt{5}x - 2y = 22 . . . . . . . . \left(i\right)

⇒T2:25x+2y+2y+4−32=0⇒ {T}_{2}: 2\sqrt{5}x + 2y + 2y + 4 - 32 = 0

⇒25x+4y=28⇒ 2\sqrt{5}x + 4y = 28

⇒T2:5x+2y=14.........(ii)⇒ {T}_{2}: \sqrt{5}x + 2y = 14 . . . . . . . . . \left(ii\right)

From \left(i\right)and(ii)and \left(ii\right)

α=185β=−2\alpha = \dfrac{18}{\sqrt{5}}\beta = - 2

⇒α2−β2=3045⇒ {\alpha}^{2} - {\beta}^{2} = \dfrac{304}{5}

Hence this is the required option.

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