Let P be the point of intersection of the common tangents to the parabola y 2 = 12 x and the hyperbola &#160…

Let P be the point of intersection of the common tangents to the parabola y2=12x and the hyperbola  8x2-y2=8. If S and S' denote the foci of the hyperbola where S lies on the positive x-axis then P divides SS' in a ratio:
  1. 5:4
  2. 2:1
  3. 13:11
  4. 14:13

Solution

Let m is slope of common tangent and an equation of tangent to hyperbola x21-y28=1 is

y=mx±1m2-8      ...1

equation of tangent to parabola y2=12x is

y=mx+3m       ...2

 1 & 2 is same

  ±m2-8=3m

m4-8m2-9=0m2=-1 (Reject)

m4-8m2-9=0m2=9m=±3

equation of common tangents is y=3x+1&y=-3x-1

point of intersection of common tangents is R-13,0 & Foci of hyperbolas are 3,0 & -3,0

-3λ+3λ+1=-13λ=54

Hence, the required ratio is 5 : 4.

Asked in: JEE Main 2019 (12 Apr Shift 1)

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