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Questions  

If the tangent at P(θ) on the ellipse 16x2+11y2=256

touches the circle  x2+y2+2x15=0, then θ

a
π6
b
π3
c
2π3
d
5π6

detailed solution

Correct option is C

Centre of the circle is (– 1, 0) and radius is 4. Equation of the tangent at P(θ) to the ellipse isx4cos⁡ θ+y16/11sin⁡ θ=1If this touches the circle, then−cos⁡ θ4−1cos2⁡ θ16+sin2⁡ θ256/11=4⇒(cos⁡ θ+4)2=256cos2⁡ θ16+11sin2⁡ θ256⇒4cos2⁡ θ−8cos⁡ θ−5=0⇒(2cos⁡ θ−5)(2cos⁡ θ+1)=0⇒cos⁡ θ=−1/2⇒θ=2π/3

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