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JEE Advanced 2021 Paper 2 · Mathematics · Conic Sections · hard

The ellipse E:(x^2/(9)+(y^2/(5)=1 and the parabola P:y^2=8x are drawn in the same plane.

One or more options correct

The ellipse E:x29+y25=1E:\dfrac{x^2}{9}+\dfrac{y^2}{5}=1 and the parabola P:y2=8xP:y^2=8x are drawn in the same plane. Which of the following statements is/are correct?
  1. A. EE and PP intersect at exactly two points
  2. B. At each common point the tangents to EE and PP are perpendicular
  3. C. Every common point is at distance 175\dfrac{17}{5} from the focus (−2,0)(-2,0) of EE
  4. D. At a common point, the tangent to EE meets the xx-axis at (9,0)(9,0)
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Answer: A, C

Substituting y2=8xy^2=8x in EE gives 5x2+72x−45=05x^2+72x-45=0, i.e. x=35x=\frac35 or x=−15x=-15. Only x=35x=\frac35 is admissible (since x≥0x\ge0 and ∣x∣≤3|x|\le3), with y=±2305y=\pm\frac{2\sqrt{30}}5, so there are exactly two points and (A) is true. The slopes are 4y\frac4y (for PP) and −5x9y-\frac{5x}{9y} (for EE); their product is −20x9y2=−20(3/5)9(24/5)=−518≠−1-\frac{20x}{9y^2}=-\frac{20(3/5)}{9(24/5)}=-\frac{5}{18}\ne-1, so (B) is false. The focus of PP is (2,0)(2,0), also a focus of EE (c2=4c^2=4); the distance from it is x+2=135x+2=\frac{13}{5}, so the sum 2a=62a=6 gives 6−135=1756-\frac{13}5=\frac{17}5 from (−2,0)(-2,0) and (C) is true. The tangent to EE cuts the axis at 9x0=15\frac{9}{x_0}=15, not 99, so (D) is false.
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