Q35 / 60 · JEE Advanced 2015 (Paper 2) · Mathematics

Let E1 and E2 be two ellipse whose centers are at the origin. The major axes of E1and E2 lie along the x - axis and the y - axis, respectively. Let S be the circle x2+y-12=2. The straight line x+y=3 touches the curves S, E1 and E2 at P, Q and R, respectively. Suppose that PQ=PR= 223. If e1 and e2 are the eccentricities of E1 and E2,respectively, then the correct expression(s) is(are)

  • Correct answer
    A
    e12+ e22=4340
  • Correct answer
    B
    e1e2= 7210
  • C
    e12- e22=58
  • D
    e1e2= 34

Solution

Let Q be (x1, y1)
So equation tangent at Q will be
xx1+yy1-y+y1-1=0
Comparing with x+y=3
x1y1 ≡(1,2)
So R and Q will be
1 ±223cos⁡3π4, 2±223sin⁡3π4
⇒  Q 53 ,43 and 13 ,83
Let Q lies on x2 a2+ y2b2=1
So tangent at P is
5x3a2+4y3b2=1
Comparing with x+y=3
a2=5, b2=4 ⇒e1=15
And R lies on x2a12+y2b12=1
So tangent at x3a12+8y3b12=3
Comparing with x+y=3
⇒   a12=1, b12=8   ⇒  e2=78
⇒   e12+e22=4340 and e1e2=7210

Hence, the correct answer is options: 'A', 'B'.

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