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NDA 2025
Exam
NDA
Year
2025
Subject
Mathematics
Chapter
Differentiation

NDA 2025 · Mathematics · Differentiation

For the following three (03) items: Let y = f(x) = x ^ -1 x 1 - x^2...

For the following three (03) items:
Let y=f(x)=xsin⁡−1x1−x2+ln⁡1−x2y = f(x) = \dfrac{x\sin^{-1} x}{\sqrt{1 - x^2}} + \ln\sqrt{1 - x^2}.

What is d2ydx2\dfrac{d^2y}{dx^2} at x=0x = 0 equal to?

Options

  1. A00
  2. B0.50.5
  3. C11
  4. D1.51.5

Correct answer

C. 11

Step-by-step solution

Given y=xsin⁡−1x1−x2+ln⁡1−x2y = \dfrac{x\sin^{-1} x}{\sqrt{1 - x^2}} + \ln\sqrt{1 - x^2}

We can rewrite the function as:
y=xsin⁡−1x1−x2+12ln⁡(1−x2)y = \dfrac{x\sin^{-1} x}{\sqrt{1 - x^2}} + \dfrac{1}{2}\ln(1 - x^2)

Differentiating with respect to xx using the quotient and chain rules:
dydx=(sin⁡−1x+x1−x2)1−x2−xsin⁡−1x(−x1−x2)1−x2+12(−2x1−x2)\dfrac{dy}{dx} = \dfrac{\left(\sin^{-1} x + \dfrac{x}{\sqrt{1 - x^2}}\right)\sqrt{1 - x^2} - x\sin^{-1} x \left(\dfrac{-x}{\sqrt{1 - x^2}}\right)}{1 - x^2} + \dfrac{1}{2} \left(\dfrac{-2x}{1 - x^2}\right)

dydx=1−x2sin⁡−1x+x+x2sin⁡−1x1−x21−x2−x1−x2\dfrac{dy}{dx} = \dfrac{\sqrt{1 - x^2}\sin^{-1} x + x + \dfrac{x^2\sin^{-1} x}{\sqrt{1 - x^2}}}{1 - x^2} - \dfrac{x}{1 - x^2}

dydx=(1−x2)sin⁡−1x+x1−x2+x2sin⁡−1x(1−x2)3/2−x1−x2\dfrac{dy}{dx} = \dfrac{(1 - x^2)\sin^{-1} x + x\sqrt{1 - x^2} + x^2\sin^{-1} x}{(1 - x^2)^{3/2}} - \dfrac{x}{1 - x^2}

dydx=sin⁡−1x+x1−x2(1−x2)3/2−x1−x2\dfrac{dy}{dx} = \dfrac{\sin^{-1} x + x\sqrt{1 - x^2}}{(1 - x^2)^{3/2}} - \dfrac{x}{1 - x^2}

dydx=sin⁡−1x(1−x2)3/2+x1−x2−x1−x2=sin⁡−1x(1−x2)3/2\dfrac{dy}{dx} = \dfrac{\sin^{-1} x}{(1 - x^2)^{3/2}} + \dfrac{x}{1 - x^2} - \dfrac{x}{1 - x^2} = \dfrac{\sin^{-1} x}{(1 - x^2)^{3/2}}

Differentiating again with respect to xx:
d2ydx2=11−x2(1−x2)3/2−sin⁡−1x⋅32(1−x2)1/2(−2x)(1−x2)3\dfrac{d^2y}{dx^2} = \dfrac{\dfrac{1}{\sqrt{1 - x^2}} (1 - x^2)^{3/2} - \sin^{-1} x \cdot \dfrac{3}{2}(1 - x^2)^{1/2}(-2x)}{(1 - x^2)^3}

d2ydx2=(1−x2)+3x1−x2sin⁡−1x(1−x2)3\dfrac{d^2y}{dx^2} = \dfrac{(1 - x^2) + 3x\sqrt{1 - x^2}\sin^{-1} x}{(1 - x^2)^3}

d2ydx2=1(1−x2)2+3xsin⁡−1x(1−x2)5/2\dfrac{d^2y}{dx^2} = \dfrac{1}{(1 - x^2)^2} + \dfrac{3x\sin^{-1} x}{(1 - x^2)^{5/2}}

Substituting x=0x = 0 into the second derivative:
\left. \dfrac{d^2y}{dx^2} \right|_{x=0} = \dfrac{1}{(1 - 0)^2} + 0 = 1<br><br>Answer:<br><br>Answer:1
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