Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Ellipse question

2024 · Shift 1 · Q21
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Advanced
  3. /Mathematics
  4. /Ellipse
  5. /2024 · Shift 1 · Q21

Ellipse question

2024 · Shift 1 · Q21

JEE AdvancedMathematicsEllipseMCQ+3 / −1
Consider the ellipse x29+y24=1\frac{x^2}{9}+\frac{y^2}{4}=19x2​+4y2​=1. Let S(p,q)S(p, q)S(p,q) be a point in the first quadrant such that p29+q24>1\frac{p^2}{9}+\frac{q^2}{4}\gt 19p2​+4q2​>1. Two tangents are drawn from SSS to the ellipse, of which one meets the ellipse at one end point of the minor axis and the other meets the ellipse at a point TTT in the fourth quadrant. Let RRR be the vertex of the ellipse with positive xxx-coordinate and OOO be the center of the ellipse. If the area of the triangle △ORT\triangle O R T△ORT is 32\frac{3}{2}23​, then which of the following options is correct?
  1. A
    q=2,p=33q=2, p=3 \sqrt{3}q=2,p=33​
  2. B
    q=2,p=43q=2, p=4 \sqrt{3}q=2,p=43​
  3. C
    q=1,p=53q=1, p=5 \sqrt{3}q=1,p=53​
  4. D
    q=1,p=63q=1, p=6 \sqrt{3}q=1,p=63​
View written solutionFree

Correct answer: A

  1. Given ellipse and key points

The ellipse is x29+y24=1\frac{x^2}{9}+\frac{y^2}{4}=19x2​+4y2​=1 so its semi-major and semi-minor axes are a=3,b=2.a=3,\quad b=2.a=3,b=2.

Hence:

  • Center: O=(0,0)O=(0,0)O=(0,0)
  • Vertex with positive xxx-coordinate: R=(3,0)R=(3,0)R=(3,0)
  • End points of minor axis: (0,2)(0,2)(0,2) and (0,−2)(0,-2)(0,−2)

Since S(p,q)S(p,q)S(p,q) is in the first quadrant and one tangent from SSS touches the ellipse at an end point of the minor axis, that tangent must be the tangent at (0,2)(0,2)(0,2) (not at (0,−2)(0,-2)(0,−2)).


  1. Tangent at the end point of minor axis

For the ellipse x29+y24=1,\frac{x^2}{9}+\frac{y^2}{4}=1,9x2​+4y2​=1, the tangent at (0,2)(0,2)(0,2) is 0⋅x9+2y4=1  ⟹  y=2.\frac{0\cdot x}{9}+\frac{2y}{4}=1 \implies y=2.90⋅x​+42y​=1⟹y=2.

Since S(p,q)S(p,q)S(p,q) lies on this tangent, we must have q=2.q=2.q=2.

So only options A and B remain.


  1. Coordinates of point TTT using area condition

Let T=(xT,yT)T=(x_T,y_T)T=(xT​,yT​) be the point of tangency in the fourth quadrant. So yT<0,xT29+yT24=1.y_T<0, \quad \frac{x_T^2}{9}+\frac{y_T^2}{4}=1.yT​<0,9xT2​​+4yT2​​=1.

Now area of triangle △ORT\triangle ORT△ORT is given as 32\frac{3}{2}23​.

Points are: O=(0,0),R=(3,0),T=(xT,yT).O=(0,0),\quad R=(3,0),\quad T=(x_T,y_T).O=(0,0),R=(3,0),T=(xT​,yT​).

Using base OR=3OR=3OR=3, the height from TTT to the xxx-axis is ∣yT∣|y_T|∣yT​∣. So Area=12⋅3⋅∣yT∣=32.\text{Area} = \frac{1}{2}\cdot 3 \cdot |y_T| = \frac{3}{2}.Area=21​⋅3⋅∣yT​∣=23​. Thus, ∣yT∣=1.|y_T|=1.∣yT​∣=1.

Since TTT is in the fourth quadrant, yT=−1.y_T=-1.yT​=−1.

Now substitute into the ellipse: xT29+(−1)24=1\frac{x_T^2}{9}+\frac{(-1)^2}{4}=19xT2​​+4(−1)2​=1 xT29+14=1\frac{x_T^2}{9}+\frac14=19xT2​​+41​=1 xT29=34\frac{x_T^2}{9}=\frac349xT2​​=43​ xT2=274x_T^2=\frac{27}{4}xT2​=427​ xT=332x_T=\frac{3\sqrt3}{2}xT​=233​​ (since fourth quadrant implies xT>0x_T>0xT​>0).

Therefore, T=(332,−1).T=\left(\frac{3\sqrt3}{2},-1\right).T=(233​​,−1).


  1. Equation of tangent at TTT

For ellipse x29+y24=1,\frac{x^2}{9}+\frac{y^2}{4}=1,9x2​+4y2​=1, the tangent at (x1,y1)(x_1,y_1)(x1​,y1​) is xx19+yy14=1.\frac{xx_1}{9}+\frac{yy_1}{4}=1.9xx1​​+4yy1​​=1.

At T=(332,−1),T=\left(\frac{3\sqrt3}{2},-1\right),T=(233​​,−1), the tangent is x(332)9+y(−1)4=1.\frac{x\left(\frac{3\sqrt3}{2}\right)}{9}+\frac{y(-1)}{4}=1.9x(233​​)​+4y(−1)​=1. Simplify: 36x−y4=1.\frac{\sqrt3}{6}x-\frac{y}{4}=1.63​​x−4y​=1.

Since S(p,q)S(p,q)S(p,q) lies on this tangent and q=2q=2q=2, 36p−24=1\frac{\sqrt3}{6}p-\frac{2}{4}=163​​p−42​=1 36p−12=1\frac{\sqrt3}{6}p-\frac12=163​​p−21​=1 36p=32\frac{\sqrt3}{6}p=\frac3263​​p=23​ p=32⋅63=93=33.p=\frac32\cdot \frac{6}{\sqrt3}=\frac{9}{\sqrt3}=3\sqrt3.p=23​⋅3​6​=3​9​=33​.

Hence, p=33,q=2.p=3\sqrt3,\quad q=2.p=33​,q=2.


  1. Check external point condition

We verify that SSS lies outside the ellipse: p29+q24=(33)29+224=279+1=3+1=4>1.\frac{p^2}{9}+\frac{q^2}{4}=\frac{(3\sqrt3)^2}{9}+\frac{2^2}{4}=\frac{27}{9}+1=3+1=4>1.9p2​+4q2​=9(33​)2​+422​=927​+1=3+1=4>1. So the condition is satisfied.


  1. Evaluate options
  • A: q=2, p=33q=2,\ p=3\sqrt3q=2, p=33​ ✅
  • B: q=2, p=43q=2,\ p=4\sqrt3q=2, p=43​ ❌
  • C: q=1, p=53q=1,\ p=5\sqrt3q=1, p=53​ ❌
  • D: q=1, p=63q=1,\ p=6\sqrt3q=1, p=63​ ❌

Therefore the correct option is A.\boxed{\text{A}}.A​.

PreviousNext

More from Ellipse

  • Let T1​ and T2​ be two distinct common tangents to the ellipse E:6x2​+3y2​=1 and the parabola P:y2=12x. Suppose that the tangent T1​ touches P and E at the points A1​ and A2​, respectively and the…2023 · Multiple correct
  • Consider the ellipse 4x2​+3y2​=1 Let H(α,0),0<α<2, be a point. A straight line drawn through H parallel to the y-axis crosses the ellipse and its auxiliary circle at points E and F… Includes table2022 · MCQ
  • Let E be the ellipse 16x2​+9y2​=1. For any three distinct points P, Q and Q' on E, let M(P, Q) be the mid-point of the line segment joining P and Q, and M(P, Q') be the mid-point of the line segment…2021 · Numerical
  • Define the collections {E1, E2, E3, ...} of ellipses and {R1, R2, R3.....} of rectangles as follows : E1​:9x2​+4y2​=1 R1 : rectangle of largest area, with sides parallel to the axes, inscribed in E1; En :…2019 · Multiple correct
  • Let S be the circle in the XY-plane defined the equation x2 + y2 = 4. Let P be a point on the circle S with both coordinates being positive. Let the tangent to S at P intersect the coordinate axes at the points M and N. Then, the mid-point…2018 · MCQ
  • Consider two straight lines, each of which is tangent to both the circle x2 + y2 = (1/2) and the parabola y2 = 4x. Let these lines intersect at the point Q. Consider the ellipse whose centre is at the origin O(0, 0) and whose semi-major…2018 · Multiple correct
  • For how many values of p, the circle x2 + y2 + 2x + 4y − p = 0 and the coordinate axes have exactly three common points?2017 · Numerical
  • Let F1​(x1​,0) and F2​(x2​,0) for x1​<0 and x2​>0, be the foci of the ellipse 9x2​+8y2​=1. Suppose a parabola having vertex at the origin and…2016 · MCQ