Q6 / 53 · NTA Abhyas (JEE Main) 2020 · Mathematics · Ellipse

A normal is drawn to the ellipse x29+y2=1 at the point 3cos⁡θ,sin⁡θ where 0<θ<π2. If N is the foot of the perpendicular from the origin O to the normal such that ON=2, then θ is equal to

  • A
    π4
  • B
    π12
  • C
    π3
  • Correct answer
    D
    π6

Solution

Equation of the normal at 3cosθ,sinθ is 3xcos⁡θ-ysin⁡θ=8
So, ON=-89sec2⁡θ+cosec2⁡θ=2 (given)
⇒16=91+tan2⁡θ+1+cot2⁡θ⇒6=6+3tan⁡θ-cot⁡θ2

⇒3tan⁡θ-cot⁡θ=0
Hence, tan2⁡θ=13⇒θ=π6

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

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