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Indefinite Integrals question

2025 · 22 Jan · Shift 2 · Q35
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  5. /2025 · 22 Jan · Shift 2 · Q35

Indefinite Integrals question

2025 · 22 Jan · Shift 2 · Q35

JEE MainMathematicsIndefinite IntegralsMCQ+4 / −1
If ∫ex(xsin⁡−1x1−x2+sin⁡−1x(1−x2)3/2+x1−x2)dx=g(x)+C\int \mathrm{e}^x\left(\frac{x \sin ^{-1} x}{\sqrt{1-x^2}}+\frac{\sin ^{-1} x}{\left(1-x^2\right)^{3 / 2}}+\frac{x}{1-x^2}\right) \mathrm{d} x=\mathrm{g}(x)+\mathrm{C}∫ex(1−x2​xsin−1x​+(1−x2)3/2sin−1x​+1−x2x​)dx=g(x)+C, where C is the constant of integration, then g(12)g\left(\frac{1}{2}\right)g(21​) equals :
  1. A
    π6e3\frac{\pi}{6} \sqrt{\frac{\mathrm{e}}{3}}6π​3e​​
  2. B
    π6e2\frac{\pi}{6} \sqrt{\frac{\mathrm{e}}{2}}6π​2e​​
  3. C
    π4e3\frac{\pi}{4} \sqrt{\frac{\mathrm{e}}{3}}4π​3e​​
  4. D
    π4e2\frac{\pi}{4} \sqrt{\frac{\mathrm{e}}{2}}4π​2e​​
View written solutionFree

Correct answer: A

  1. We need to evaluate
∫ex(xsin⁡−1x1−x2+sin⁡−1x(1−x2)3/2+x1−x2)dx=g(x)+C.\int e^x\left(\frac{x\sin^{-1}x}{\sqrt{1-x^2}}+\frac{\sin^{-1}x}{(1-x^2)^{3/2}}+\frac{x}{1-x^2}\right)dx=g(x)+C.∫ex(1−x2​xsin−1x​+(1−x2)3/2sin−1x​+1−x2x​)dx=g(x)+C.

We will try to recognize the integrand as the derivative of a product involving exe^xex.

  1. Let
f(x)=sin⁡−1x1−x2.f(x)=\frac{\sin^{-1}x}{\sqrt{1-x^2}}.f(x)=1−x2​sin−1x​.

Then

ddx(exf(x))=ex(f(x)+f′(x)).\frac{d}{dx}\big(e^x f(x)\big)=e^x\big(f(x)+f'(x)\big).dxd​(exf(x))=ex(f(x)+f′(x)).

So we compute f′(x)f'(x)f′(x).

  1. Differentiate
f(x)=sin⁡−1x (1−x2)−1/2.f(x)=\sin^{-1}x\,(1-x^2)^{-1/2}.f(x)=sin−1x(1−x2)−1/2.

Using product rule,

f′(x)=11−x2⋅(1−x2)−1/2+sin⁡−1x⋅ddx(1−x2)−1/2.f'(x)=\frac{1}{\sqrt{1-x^2}}\cdot (1-x^2)^{-1/2}+\sin^{-1}x\cdot \frac{d}{dx}(1-x^2)^{-1/2}.f′(x)=1−x2​1​⋅(1−x2)−1/2+sin−1x⋅dxd​(1−x2)−1/2.

Now,

11−x2⋅(1−x2)−1/2=11−x2,\frac{1}{\sqrt{1-x^2}}\cdot (1-x^2)^{-1/2}=\frac{1}{1-x^2},1−x2​1​⋅(1−x2)−1/2=1−x21​,

and

ddx(1−x2)−1/2=x(1−x2)3/2.\frac{d}{dx}(1-x^2)^{-1/2}=\frac{x}{(1-x^2)^{3/2}}.dxd​(1−x2)−1/2=(1−x2)3/2x​.

Hence

f′(x)=11−x2+xsin⁡−1x(1−x2)3/2.f'(x)=\frac{1}{1-x^2}+\frac{x\sin^{-1}x}{(1-x^2)^{3/2}}.f′(x)=1−x21​+(1−x2)3/2xsin−1x​.
  1. Therefore,
f(x)+f′(x)=sin⁡−1x1−x2+11−x2+xsin⁡−1x(1−x2)3/2.f(x)+f'(x)=\frac{\sin^{-1}x}{\sqrt{1-x^2}}+\frac{1}{1-x^2}+\frac{x\sin^{-1}x}{(1-x^2)^{3/2}}.f(x)+f′(x)=1−x2​sin−1x​+1−x21​+(1−x2)3/2xsin−1x​.

This is not exactly in the given form. So let us instead try

f(x)=xsin⁡−1x1−x2.f(x)=\frac{x\sin^{-1}x}{\sqrt{1-x^2}}.f(x)=1−x2​xsin−1x​.

Then

ddx(exf(x))=ex(f+f′).\frac{d}{dx}\big(e^x f(x)\big)=e^x(f+f').dxd​(exf(x))=ex(f+f′).

Now compute f′(x)f'(x)f′(x).

  1. Let
f(x)=xsin⁡−1x (1−x2)−1/2.f(x)=x\sin^{-1}x\,(1-x^2)^{-1/2}.f(x)=xsin−1x(1−x2)−1/2.

Differentiate using product rule:

f′(x)=sin⁡−1x(1−x2)−1/2+x⋅11−x2⋅(1−x2)−1/2+xsin⁡−1x⋅x(1−x2)3/2.f'(x)=\sin^{-1}x(1-x^2)^{-1/2}+x\cdot \frac{1}{\sqrt{1-x^2}}\cdot (1-x^2)^{-1/2}+x\sin^{-1}x\cdot \frac{x}{(1-x^2)^{3/2}}.f′(x)=sin−1x(1−x2)−1/2+x⋅1−x2​1​⋅(1−x2)−1/2+xsin−1x⋅(1−x2)3/2x​.

Simplify:

f′(x)=sin⁡−1x1−x2+x1−x2+x2sin⁡−1x(1−x2)3/2.f'(x)=\frac{\sin^{-1}x}{\sqrt{1-x^2}}+\frac{x}{1-x^2}+\frac{x^2\sin^{-1}x}{(1-x^2)^{3/2}}.f′(x)=1−x2​sin−1x​+1−x2x​+(1−x2)3/2x2sin−1x​.

Thus

f+f'= rac{x\sin^{-1}x}{\sqrt{1-x^2}}+\frac{\sin^{-1}x}{\sqrt{1-x^2}}+\frac{x}{1-x^2}+\frac{x^2\sin^{-1}x}{(1-x^2)^{3/2}}.

Combine the two terms containing sin⁡−1x\sin^{-1}xsin−1x:

xsin⁡−1x1−x2+x2sin⁡−1x(1−x2)3/2=xsin⁡−1x(1−x2)+x2sin⁡−1x(1−x2)3/2=xsin⁡−1x(1−x2)3/2.\frac{x\sin^{-1}x}{\sqrt{1-x^2}}+\frac{x^2\sin^{-1}x}{(1-x^2)^{3/2}} =\frac{x\sin^{-1}x(1-x^2)+x^2\sin^{-1}x}{(1-x^2)^{3/2}} =\frac{x\sin^{-1}x}{(1-x^2)^{3/2}}.1−x2​xsin−1x​+(1−x2)3/2x2sin−1x​=(1−x2)3/2xsin−1x(1−x2)+x2sin−1x​=(1−x2)3/2xsin−1x​.

So

f+f'= rac{x\sin^{-1}x}{(1-x^2)^{3/2}}+\frac{\sin^{-1}x}{\sqrt{1-x^2}}+\frac{x}{1-x^2}.

Still not matching the given integrand directly.

  1. Now observe the given first two terms:
xsin⁡−1x1−x2+sin⁡−1x(1−x2)3/2.\frac{x\sin^{-1}x}{\sqrt{1-x^2}}+\frac{\sin^{-1}x}{(1-x^2)^{3/2}}.1−x2​xsin−1x​+(1−x2)3/2sin−1x​.

Factor sin⁡−1x\sin^{-1}xsin−1x:

sin⁡−1x(x1−x2+1(1−x2)3/2)=sin⁡−1x⋅x(1−x2)+1(1−x2)3/2.\sin^{-1}x\left(\frac{x}{\sqrt{1-x^2}}+\frac{1}{(1-x^2)^{3/2}}\right) =\sin^{-1}x\cdot \frac{x(1-x^2)+1}{(1-x^2)^{3/2}}.sin−1x(1−x2​x​+(1−x2)3/21​)=sin−1x⋅(1−x2)3/2x(1−x2)+1​.

This does not suggest immediate simplification, so let us instead check derivative of

F(x)=ex⋅sin⁡−1x1−x2.F(x)=e^x\cdot \frac{\sin^{-1}x}{\sqrt{1-x^2}}.F(x)=ex⋅1−x2​sin−1x​.

From step 3,

F′(x)=ex(sin⁡−1x1−x2+11−x2+xsin⁡−1x(1−x2)3/2).F'(x)=e^x\left(\frac{\sin^{-1}x}{\sqrt{1-x^2}}+\frac{1}{1-x^2}+\frac{x\sin^{-1}x}{(1-x^2)^{3/2}}\right).F′(x)=ex(1−x2​sin−1x​+1−x21​+(1−x2)3/2xsin−1x​).

Now compare this with the given integrand. At this stage, it is natural to suspect a typographical mismatch in the first term of the question, because the standard exact derivative structure is

ex(xsin⁡−1x(1−x2)3/2+sin⁡−1x1−x2+11−x2),e^x\left(\frac{x\sin^{-1}x}{(1-x^2)^{3/2}}+\frac{\sin^{-1}x}{\sqrt{1-x^2}}+\frac{1}{1-x^2}\right),ex((1−x2)3/2xsin−1x​+1−x2​sin−1x​+1−x21​),

which integrates to exsin⁡−1x1−x2e^x\dfrac{\sin^{-1}x}{\sqrt{1-x^2}}ex1−x2​sin−1x​.

  1. Since the options involve only a clean value with sin⁡−1(1/2)=π/6\sin^{-1}(1/2)=\pi/6sin−1(1/2)=π/6 and 1−(1/2)2=3/2\sqrt{1-(1/2)^2}=\sqrt{3}/21−(1/2)2​=3​/2, let us evaluate
g(12)=e1/2⋅sin⁡−1(1/2)1−1/4=e⋅π/63/2.g\left(\frac12\right)=e^{1/2}\cdot \frac{\sin^{-1}(1/2)}{\sqrt{1-1/4}} =\sqrt e\cdot \frac{\pi/6}{\sqrt{3}/2}.g(21​)=e1/2⋅1−1/4​sin−1(1/2)​=e​⋅3​/2π/6​.

Simplify:

π6⋅e⋅23=πe33=π3e3.\frac{\pi}{6}\cdot \sqrt e\cdot \frac{2}{\sqrt3} =\frac{\pi\sqrt e}{3\sqrt3} =\frac{\pi}{3}\sqrt{\frac e3}.6π​⋅e​⋅3​2​=33​πe​​=3π​3e​​.

This value is not among the options.

  1. Let us instead test the expression
g(x)=ex/2sin⁡−1x,g(x)=e^{x/2}\sin^{-1}x,g(x)=ex/2sin−1x,

whose value at x=1/2x=1/2x=1/2 is

g(12)=e1/4⋅π6=π6e4,g\left(\frac12\right)=e^{1/4}\cdot \frac{\pi}{6}=\frac{\pi}{6}\sqrt[4]{e},g(21​)=e1/4⋅6π​=6π​4e​,

not among the options.

  1. The stored answer is option A:
π6e3.\frac{\pi}{6}\sqrt{\frac e3}.6π​3e​​.

That equals

πe63.\frac{\pi\sqrt e}{6\sqrt3}.63​πe​​.

This would arise from

e⋅π63,\sqrt e\cdot \frac{\pi}{6\sqrt3},e​⋅63​π​,

which is exactly half of the natural value from e1/2sin⁡−1x1−x2e^{1/2}\dfrac{\sin^{-1}x}{\sqrt{1-x^2}}e1/21−x2​sin−1x​ at x=1/2x=1/2x=1/2.

  1. Therefore, the printed integrand and the options are inconsistent as written. Using the standard derivative pattern, the antiderivative should be
g(x)=exsin⁡−1x1−x2,g(x)=e^x\frac{\sin^{-1}x}{\sqrt{1-x^2}},g(x)=ex1−x2​sin−1x​,

which gives

g(12)=π3e3.g\left(\frac12\right)=\frac{\pi}{3}\sqrt{\frac e3}.g(21​)=3π​3e​​.

This does not match any option, including the stored answer.

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