Q. 203.7( 3 Votes )

If 𝒳 = (2 cos θ – cos 2θ) and = (2sin θ – sin 2θ), find .

Answer :

here we have to find the double derivative, so to find double derivative we will just differentiate the first derivative once again with a similar method.

Theorem: y and x are given in a different variable that is θ . We can find by finding and and then dividing them to get the required thing.


= 2cosθ – 2cos2θ ………..(1)

= -2sinθ + 2sin2θ ……….(2)

Dividing (1) and (2), we get


{as shown in question no. 18}


To find f’’ we will differentiate f’ with θ and then divide with equation (2).



Now divide by equation (2).

Putting θ = π/2

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