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1)

 Suppose that the foci of the ellipse   x29+y25=1  are (f1,0) and (f2, o) where f1>0 and f2<0 . Let P1   and P2 be two parabolas with a common vertex at (0,0) with foci at (f1,0) and (2f2,0)  respectively  .Let T1 be a tangent to P1 which passes through (2 f2,o) and T2 be  a tangent to P2. P2 which passes through (f1,0) . If m1 is the slop of T1  and m2 is the slope of T2, then the value of  (1m21+m22)  is


A) 2

B) 4

C) 3

D) 5

Answer:

Option B

Explanation:

1132021124_m1.JPG

Tangent to P1 passes through

   (2f2,0)i.e, (-4,0)

  T1:y=m1x+2m1

               0=4m1+2m1

        m21=1/2     ..........(i)

Also, tangent to  P2   passes through (f1,0) i.e, (2,0)

                     T2:y=m2x+(4)m2

                     0=2m24m2

               m22=2

      1m21+m22=2+2=4