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Question: Answered & Verified by Expert
The tangent and normal to the ellipse 3x2+5y2=32 at the point P2, 2 meet the x-axis at Q and R, respectively. Then the area (in sq. units) of the triangle PQR is:
MathematicsEllipseJEE MainJEE Main 2019 (10 Apr Shift 2)
Options:
  • A 6815
  • B 163
  • C 143
  • D 3415
Solution:
2110 Upvotes Verified Answer
The correct answer is: 6815

The equation of tangent and normal to the ellipse x2a2+y2b2=1 at a point x1, y1 are respectively xx1a2+yy1b2=1 and a2xx1-b2yy1=a2-b2.

The given ellipse is 3x2+5y2=32,  3x232+5y232=1.

Hence, the tangent and normal to the ellipse 3x232+5y232=1 at 2, 2 are respectively 3×2×x32+5×2×y32=1 and 32×x3×2-32×y5×2=323-325

Hence, the tangent is 3x+5y=16   ...1

And, the normal is 5x-3y=4     ...2

The point where the tangent meets the x-axis can be obtained by putting y=0, 3x+0=16  x=163, thus the point Q163, 0.

Similarly, the point where the normal meets the x-axis, is x=45, thus the point R43, 0. 

Tangent and normal intersect at P2, 2, and the length of perpendicular from any point on x-axis is the absolute value of its y-co-ordinate, hence the height of the triangle is 2 units.

And, hence the required area is =12QR×h

=12×163-45×2=6815 sq units.

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