Skip to content
Question of 281

Q.Differentiate sec⁡−112x2−1\sec^{-1}\dfrac{1}{2x^2-1} with respect to 1−x2\sqrt{1-x^2}.

Odisha ChseOdisha CHSE +2 Science Board Exam 2020Subjective· 4mImportance★★★★★
0% · 0/281 Questions
🔒 Locked · start free trial →

You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.

Start your 14-day free trial to unlock the full solution →

Substituting x=cos⁡θx=\cos\theta turns both expressions into simple functions of θ\theta; the ratio of derivatives comes out to 2/x2/x.

Let u=sec⁡−112x2−1u=\sec^{-1}\dfrac{1}{2x^2-1} and v=1−x2v=\sqrt{1-x^2}. Put x=cos⁡θx=\cos\theta, θ∈(0,π)\theta\in(0,\pi).

Then 2x2−1=2cos⁡2θ−1=cos⁡2θ2x^2-1=2\cos^2\theta-1=\cos2\theta, so 12x2−1=1cos⁡2θ=sec⁡2θ\dfrac1{2x^2-1}=\dfrac1{\cos2\theta}=\sec2\theta.

u=sec⁡−1(sec⁡2θ)=2θ=2cos⁡−1x.u=\sec^{-1}(\sec2\theta)=2\theta=2\cos^{-1}x.

Also v=1−x2=1−cos⁡2θ=sin⁡θv=\sqrt{1-x^2}=\sqrt{1-\cos^2\theta}=\sin\theta, but for differentiation it's simplest to keep v=1−x2v=\sqrt{1-x^2} directly as a function of xx.

…

Unlock everything free for 14 days

  • Full step-by-step solutions
  • Concept-first explanations
  • Methods, shortcuts & mistakes
  • PYQ mapping + timed mock tests

Full access for 14 days. No credit card required.