Suppose that the foci of the ellipse x 2 9 +   y 2 5 = 1 are f 1 ,   0   a n d   ( f 2 ,…

Suppose that the foci of the ellipse x29+ y25=1 are f1, 0 and (f2, 0) where f1>0 and f2<0. Let P1 and P2 be two parabolas with a common vertex at (0, 0) and with foci at f1, 0 and 2f2, 0, respectively. Let T1 be a tangent to P1 which passes through 2f2, 0 and T2 be a tangent to P2 which passes through (f1, 0) . If m1 is the slope of T1 and m2  is the slope of T2, then the value of 1m12+ m22 is

Solution



f1 (2, 0)
f2 (-2, 0)
Parabolas are
y2= 8x
y2= -16x
T1 :y=mx+2m
0= -4m+2m
  m2=12
T2 :y=mx-4m
2m-4m=0
  m2=2
Now, m22+ 1m12=2+2=4

Asked in: JEE Advanced 2015 (Paper 2)

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