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JEE Main 202131 AugustEvening Shift
Exam
JEE Main
Year
2021
Date
31 August
Shift
Evening Shift
Subject
Mathematics
Chapter
Ellipse

JEE Main 2021 · 31 August · Evening Shift · Mathematics · Ellipse

The locus of mid-points of the line segments joining (- 3, - 5) and...

The locus of mid-points of the line segments joining (−3,−5)\left(- 3, - 5\right) and the points on the ellipse x24+y29=1\dfrac{{x}^{2}}{4} + \dfrac{{y}^{2}}{9} = 1 is :

Options

  1. A36x2+16y2+90x+56y+145=036{x}^{2} + 16{y}^{2} + 90x + 56y + 145 = 0
  2. B36x2+16y2+108x+80y+145=036{x}^{2} + 16{y}^{2} + 108x + 80y + 145 = 0
  3. C9x2+4y2+18x+8y+145=09{x}^{2} + 4{y}^{2} + 18x + 8y + 145 = 0
  4. D36x2+16y2+72x+32y+145=036{x}^{2} + 16{y}^{2} + 72x + 32y + 145 = 0

Correct answer

B. 36x2+16y2+108x+80y+145=036{x}^{2} + 16{y}^{2} + 108x + 80y + 145 = 0

Step-by-step solution

Parametric point on the given ellipse is (2sinθ,3cosθ)\left(2sin\theta, 3cos\theta\right)

Let, the mid-point of line segments joining \left(- 3, - 5\right)and(2sinθ,3cosθ)and \left(2sin\theta, 3cos\theta\right) is \left(h, k\right)</p><p>Then,byusingmid−pointformula,weget</p><p></p><p>Then, by using mid-point formula, we get</p><p>\dfrac{2sin\theta - 3}{2} = h, \dfrac{3cos\theta - 5}{2} = k</p><p></p><p>⇒ 2sin\theta = 2h + 3, 3cos\theta = 2k + 5</p><p></p><p>⇒ sin\theta = \dfrac{2h + 3}{2}, cos\theta = \dfrac{2k + 5}{3}</p><p>Weknow,</p><p>We know,\sin^{2}\theta + \cos^{2}\theta = 1</p><p></p><p>⇒ {\left(\dfrac{2h + 3}{2}\right)}^{2} + {\left(\dfrac{2k + 5}{3}\right)}^{2} = 1</p><p></p><p>⇒ \dfrac{1}{4}\left[4{h}^{2} + 9 + 12h\right] + \dfrac{1}{9}\left[4{k}^{2} + 25 + 20k\right] = 1</p><p></p><p>⇒ 36{h}^{2} + 16{k}^{2} + 108h + 80k + 145 = 0</p><p>Hence,thelocusof(x,y)</p><p>Hence, the locus of \left(x, y\right) is 36x2+16y2+108x+80y+145=036{x}^{2} + 16{y}^{2} + 108x + 80y + 145 = 0

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