Engineering
Mathematics
Normal to Ellipse
Question

If the normal to the ellipse 3x2 + 4y2 = 12 at a point P on it is parallel to the line, 2x + y = 4 and the tangent to the ellipse at P passes through Q(4, 4) then PQ is equal to

1572

2212

612

552

JEE Advance
College PredictorLive

Know your College Admission Chances Based on your Rank/Percentile, Category and Home State.

Get your JEE Main Personalised Report with Top Predicted Colleges in JoSA

Solution

3x2 + 4y2 = 12

x24+y23=1

x=2cosθ,  y=3sinθ

Equation   of  normal  isa2xx1−b2yy1=a2−b2

2xsinθ−3cosθy=sinθcosθ

Slope23tanθ=−2          ∴tanθ=−3

Equation of tangent is it passes through (4, 4)

3xcosθ+23sinθy=6

12cosθ+83sinθ=6

cosθ=−12,  sinθ=32∴  θ=120°

P(−1,22),Q(4,4)

PQ=552