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If x and y are connected parametrically by the equation without eliminating the parameter, find dydx. x = cos θ – cos 2θ, y = sin θ – sin 2θ - Mathematics

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Question

If x and y are connected parametrically by the equation without eliminating the parameter, find `dy/dx`.

x = cos θ – cos 2θ, y = sin θ – sin 2θ

Sum

Solution

Given, x `= cos theta - cos 2 theta`  and `y = sin theta - sin 2 theta`

x `= cos theta - cos 2 theta` 

Differentiating both sides with respect to θ,

`dx/(d theta) = - sin theta - (- sin 2  theta) d/(d theta) (2  theta) = - sin theta + 2 sin 2  theta`

and  y = `sin theta -  sin 2  theta)`

`therefore dy/(d theta) = cos theta -  cos 2  theta  d/(d"theta) (2  theta) = cos theta - 2 cos 2  theta`

Hence, `dy/dx = (dy/(d theta))/(dx/(d theta))`

`= (cos theta - 2 cos 2 theta)/(- sin theta + 2 sin 2 theta)`

`= (cos theta - 2 cos 2 theta)/(- (sin theta - 2 sin 2 theta))`

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Chapter 5: Continuity and Differentiability - Exercise 5.6 [Page 181]

APPEARS IN

NCERT Mathematics [English] Class 12
Chapter 5 Continuity and Differentiability
Exercise 5.6 | Q 5 | Page 181

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