The locus of the foot of perpendicular drawn from the centre of the ellipse x 2 + 3 y 2 = 6 on any tangent…

The locus of the foot of perpendicular drawn from the centre of the ellipse x2+3y2=6 on any tangent to it is
  1. x2-y22=6x2+2y2
  2. x2-y22=6x2-2y2
  3. x2+y22=6x2+2y2
  4. x2+y22=6x2-2y2

Solution

We have,

x2+3y2=6

x26+y22=1

Centre of an ellipse is 0,0.

Let the foot of perpendicular be (h,k).

Equation of tangent in slope form to the standard ellipse x2a2+y2b2=1 is

y=mx±a2m2+b2.

Hence, equation of tangent with slope m passing (h,k) is 

y=mx±6m2+2

k=mh±6m2+2, where m=-hk.

k=h-hk±6m2+2

6h2k2+2=h2+k2k

6h2+2k2=h2+k22

So, required locus is

6x2+2y2=x2+y22.

Asked in: BITSAT 2019

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