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JEE Main 20198 AprilMorning Shift
Exam
JEE Main
Year
2019
Date
8 April
Shift
Morning Shift
Subject
Mathematics
Chapter
Ellipse

JEE Main 2019 · 8 April · Morning Shift · Mathematics · Ellipse

Let O(0,0) and A(0,1) be two fixed points. Then, the locus of a...

Let O(0,0)O\left(0,0\right) and A(0,1)A\left(0,1\right) be two fixed points. Then, the locus of a point PP such that the perimeter of δAOP\delta AOP is 44 isLet O(0,0) and A(0,1) be two fixed points. Then, the locus of a point P such that the perimeter of AOP is 4 is

Options

  1. A8x2+9y2−9y=188{x}^{2} + 9{y}^{2} - 9y = 18
  2. B9x2−8y2+8y=169{x}^{2} - 8{y}^{2} + 8y = 16
  3. C8x2−9y2+9y=188{x}^{2} - 9{y}^{2} + 9y = 18
  4. D9x2+8y2−8y=169{x}^{2} + 8{y}^{2} - 8y = 16

Correct answer

D. 9x2+8y2−8y=169{x}^{2} + 8{y}^{2} - 8y = 16

Step-by-step solution

Let O(0,0) and A(0,1) be two fixed points. Then, the locus of a point P such that the perimeter of AOP is 4 is
Given, OA+PO+PA=4OA + PO + PA = 4

⇒PO+PA=3⇒ PO + PA = 3

⇒⇒Locus of PP is ellipse with foci at OO & AA and major

axis \left(2b\right) = 3</p><p>Distancebetweenfoci</p><p>Distance between foci= 2be = 1 ⇒ e = \dfrac{1}{3}</p><p></p><p>⇒MinoraxisMinor axis2a = 2b\sqrt{1 - {e}^{2}} = 3 . \dfrac{2\sqrt{2}}{3} = 2\sqrt{2}</p><p></p><p>⇒EquationofLocusofEquation of Locus ofPis:</p><p>is :</p><p>\dfrac{{x}^{2}}{8} + \dfrac{{\left(y - \dfrac{1}{2}\right)}^{2}}{9} = \dfrac{1}{4}</p><p>Bysimplifyingtheaboveequation,weget</p><p></p><p>By simplifying the above equation, we get</p><p>9{x}^{2} + 8{y}^{2} - 8y = 16

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