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Question: Answered & Verified by Expert
The normal at a point θ to the curve x=a1+cosθ,y=asinθ always passes through the fixed point
MathematicsApplication of DerivativesTS EAMCETTS EAMCET 2018 (04 May Shift 1)
Options:
  • A 0,a
  • B 2a,0
  • C a,0
  • D a,a
Solution:
2701 Upvotes Verified Answer
The correct answer is: a,0

Given that, 

x=a1+cosθ

y=asinθ

Now,

dydx=dydθdxdθ

dydx=ddθasinθddθa1+cosθ

dydx=acosθ-asinθ

dydx=-cotθ

Equation of normal at x1y1 is

y-y1=-1dydxx-x1

y-asinθ=-1-cotθx-a1+cosθ

y-asinθ=x-a-cosθcotθ

y-asinθx-a-acosθ=sinθcosθ

y-asinθsinθ=x-a-acosθcosθ

ysinθ-asinθsinθ=xcosθ-acosθ-acosθcosθ

ysinθ-a=xcosθ-acosθ-a

ysinθ=x-acosθ

Now by verifying options, a,0 satisfies the above condition

 The curve passes through a,0.

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