Q41 / 53 · NTA Abhyas (JEE Main) 2020 · Mathematics · Ellipse

If two points are taken on the minor axis of the ellipse x225+y29=1 at the same distance from the centre as the foci, then the sum of the squares of the perpendicular distances from these points on any tangent to the ellipse is

  • A
    25
  • B
    18
  • Correct answer
    C
    50
  • D
    80

Solution

Given ellipse is x225+y29=1 … 1
e=1-925=45 
S0,545=S(0,4)
S'0,-545=S'(0,-4)
Figure
Let, the tangent to the ellipse be y=mx+25m2+9 where, m is a parameter.

Now, the sum of the squares of ⊥ distances on this tangent from the points S and S' is
=m0-4+25m2+9m2+12+m0+4+25m2+9m2+12
=2(m2+1)42+(25m2+9)=50

Hence, the correct answer is option: 'C'.

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