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What will be the value of dy/dx if x = asec^2θ and y = atan^3θ at θ = π/4?(a) 1/2(b) 3/4(c) 3/2(d) 1/4The question was asked in a job interview.This question is from First Order Derivative in section Limits and Derivatives of Mathematics – Class 11

Answer»

Correct ANSWER is (C) 3/2

Explanation: Since, X = asec^2θ,

Therefore, dx/dθ = a*d/dx(sec^2θ)

= 2asecθ*secθ tanθ

Again, dy/dθ = a*d/dx(TAN^3θ)

= a * 3 tan^2θ * d/dθ(tanθ)

= 3a tan^2θ sec^2θ

 Therefore, dy/dx = (dy/dθ)/(dx/dθ)

= 3a tan^2θ sec^2θ/2asecθ*secθ tanθ

Thus, at θ = π/4 we have,

dy/dx = 3/2(tan π/4)

= 3/2



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