Q.Integrate the function $\frac{3x^2}{x^6+1}$

Showing the 12 most recent of 51 on this concept.

1. AP EAPCET 2025Set eng-2025-05-22-FN1 markMCQ
   Q.$\int\frac{x^4 - 1}{x^2\sqrt{x^4 + x^2 + 1}}dx =$ (A) $\frac{2\sqrt{x^4+x^2+1}}{x} + c$ (B) $\frac{\sqrt{x^4+x^2+1}}{x} + c$ (C) $\frac{\sqrt{x^4+x^2+1}}{2x} + c$ (D) $\frac{4\sqrt{x^4+x^2+1}}{x} + c$

   ›Reveal solutionSolution

   Differentiating the candidate $\frac{\sqrt{x^4+x^2+1}}{x}$ reproduces the given integrand exactly, confirming it as the antiderivative.

   Concept and Intuition

   When an integrand looks like it could come from a quotient rule (a square root over a power of $x$), it is often faster to differentiate a plausible candidate of that shape and check, rather than search for a substitution from scratch.

   Step-by-Step Solution

   1. Try $g(x)=\dfrac{\sqrt{x^4+x^2+1}}{x}=\dfrac{N}{x}$ where $N=\sqrt{x^4+x^2+1}$.
   2. $N'=\dfrac{4x^3+2x}{2\sqrt{x^4+x^2+1}}=\dfrac{x(2x^2+1)}{N}$.
   3. Quotient rule: $g'(x)=\dfrac{N'x-N}{x^2}=\dfrac{\frac{x^2(2x^2+1)}{N}-N}{x^2}=\dfrac{x^2(2x^2+1)-N^2}{Nx^2}$.
   4. $N^2=x^4+x^2+1$, so the numerator is $x^2(2x^2+1)-(x^4+x^2+1)=2x^4+x^2-x^4-x^2-1=x^4-1$.
   5. So $g'(x)=\dfrac{x^4-1}{x^2\sqrt{x^4+x^2+1}}$ — exactly the given integrand.
   6. Hence $\displaystyle\int\frac{x^4-1}{x^2\sqrt{x^4+x^2+1}}\,dx=\frac{\sqrt{x^4+x^2+1}}{x}+c$.

   Common Mistakes

   • Attempting a substitution like $t=x-1/x$ or $t=x+1/x$ and getting tangled in cross terms instead of recognising the quotient-rule shape.
   • Dropping the $x^2$ in the denominator when differentiating $N/x$ (quotient rule, not just $N'/x$).

   ✓Final answer

   The correct option is (B) — $\frac{\sqrt{x^4+x^2+1}}{x} + c$.

   ANSWER: B

2. AP EAPCET 2026Set eng-2026-05-13-AN1 markMCQ
   Q.$\displaystyle\int \dfrac{dx}{x^2(x^4+1)^{3/4}}=$ (A) $\left(1+\dfrac{1}{x^4}\right)^{3/4}+c$ (B) $\left(1+\dfrac{1}{x^6}\right)^{1/2}+c$ (C) $-\left(1+\dfrac{1}{x^4}\right)^{-1/4}+c$ (D) $-\left(1+\dfrac{1}{x^4}\right)^{1/4}+c$

   ›Reveal solutionSolution

   Pulling $x^4$ out from under the radical and substituting $t=1+x^{-4}$ reduces the integral to a simple power rule, giving $-(1+1/x^4)^{1/4}+c$.

   Concept and Intuition

   When the integrand has $(x^n+1)^p$, it often helps to factor out the highest power of $x$ from inside the bracket so that a substitution like $t = 1+x^{-n}$ produces a clean differential matching the rest of the integrand.

   Step-by-Step Solution

   1. Write $(x^4+1)^{3/4} = \left(x^4\left(1+\dfrac{1}{x^4}\right)\right)^{3/4} = x^3\left(1+\dfrac{1}{x^4}\right)^{3/4}$.
   2. So $\dfrac{1}{x^2(x^4+1)^{3/4}} = \dfrac{1}{x^2\cdot x^3\left(1+\frac{1}{x^4}\right)^{3/4}} = \dfrac{1}{x^5\left(1+\frac{1}{x^4}\right)^{3/4}} = x^{-5}\left(1+x^{-4}\right)^{-3/4}$.
   3. Let $t = 1+x^{-4}$. Then $dt = -4x^{-5}dx$, so $x^{-5}dx = -\dfrac{dt}{4}$.
   4. The integral becomes $\displaystyle\int t^{-3/4}\left(-\dfrac{dt}{4}\right) = -\dfrac14\cdot\dfrac{t^{1/4}}{1/4}+c = -t^{1/4}+c$.
   5. Substituting back: $-\left(1+\dfrac{1}{x^4}\right)^{1/4}+c$.

   Common Mistakes

   • Forgetting the negative sign that comes from $dt=-4x^{-5}dx$.
   • Not factoring $x^4$ out correctly before substituting, leading to a mismatched power.

   ✓Final answer

   The correct option is (D) — $-\left(1+\dfrac{1}{x^4}\right)^{1/4}+c$.

   ANSWER: D

3. AP EAPCET 2026Set eng-2026-05-14-FN1 markMCQ
   Q.$\displaystyle\int \dfrac{\sin^2 x \cos^2 x}{\cos^6 x + \sin^6 x}\,dx =$ (A) $\dfrac{1}{2}\mathrm{Tan}^{-1}(\tan^2 x) + c$ (B) $\dfrac{1}{3}\mathrm{Tan}^{-1}(\tan^2 x) + c$ (C) $\dfrac{1}{3}\mathrm{Tan}^{-1}(\tan^3 x) + c$ (D) $\mathrm{Tan}^{-1}(\tan^3 x) + c$

   ›Reveal solutionSolution

   Dividing through by $\cos^6x$ to introduce $\tan x$, then a double substitution ($t=\tan x$, then $u=t^3$), reduces the integral to a standard arctangent form, giving $\dfrac13\mathrm{Tan}^{-1}(\tan^3x)+c$.

   Concept and Intuition

   When an integrand has $\sin$ and $\cos$ appearing only in even powers that can be grouped, dividing everything by the highest power of $\cos x$ converts the whole expression into a rational function purely of $\tan x$ — a very common trick that opens the door to the substitution $t=\tan x$. Here, since the denominator naturally forms $1+\tan^6x$, a further substitution $u=t^3$ turns it into the standard $\int\frac{du}{1+u^2}$ arctangent integral.

   Step-by-Step Solution

   1. Divide numerator and denominator of $\dfrac{\sin^2x\cos^2x}{\cos^6x+\sin^6x}$ by $\cos^6x$: numerator becomes $\dfrac{\sin^2x\cos^2x}{\cos^6x} = \dfrac{\sin^2x}{\cos^4x} = \tan^2x\sec^2x$; denominator becomes $1 + \tan^6x$.
   2. The integral is now $\displaystyle\int \dfrac{\tan^2x\sec^2x}{1+\tan^6x}\,dx$.
   3. Substitute $t=\tan x$, so $dt = \sec^2x\,dx$. The integral becomes $\displaystyle\int\dfrac{t^2}{1+t^6}\,dt$.
   4. Substitute $u = t^3$, so $du = 3t^2\,dt$, i.e. $t^2\,dt = \dfrac{du}{3}$. The integral becomes $\dfrac13\displaystyle\int\dfrac{du}{1+u^2}$.
   5. This is the standard arctangent integral: $\dfrac13\mathrm{Tan}^{-1}(u) + c$.
   6. Substitute back $u=t^3=\tan^3x$: the answer is $\dfrac13\mathrm{Tan}^{-1}(\tan^3x)+c$.

   Common Mistakes

   • Mis-simplifying $\dfrac{\sin^2x\cos^2x}{\cos^6x}$ (arithmetic slip in exponents), which changes the power of $\tan x$ obtained.
   • Forgetting the second substitution ($u=t^3$) and trying to directly integrate $\int\frac{t^2}{1+t^6}dt$ as though it were already a standard arctan form.

   ✓Final answer

   The correct option is (C) — $\dfrac{1}{3}\mathrm{Tan}^{-1}(\tan^3 x) + c$.

   ANSWER: C

4. AP EAPCET 2025Set eng-2025-05-23-AN1 markMCQ
   Q.If $\displaystyle\int (x^6 + x^4 + x^2)\sqrt{2x^4 + 3x^2 + 6}\,dx = f(x) + c$, then $f(3) =$ (A) $\dfrac{3}{2}(95)^{3/2}$ (B) $\dfrac{3}{2}(195)^{3/2}$ (C) $\dfrac{3}{2}(265)^{3/2}$ (D) $\dfrac{3}{2}(175)^{3/2}$

   ›Reveal solutionSolution

   Guess the antiderivative in the form $(ax^3+bx)(2x^4+3x^2+6)^{3/2}$, match

   coefficients by differentiating, solve for $a,b$, then evaluate at $x=3$ to get

   $f(3)=\dfrac32(195)^{3/2}$.

   Concept and Intuition

   When an integrand is a polynomial times the square root of another polynomial,

   and the polynomial factor's degree matches what you'd get by differentiating a

   $(\text{poly})\cdot(\text{radicand})^{3/2}$ ansatz, the fastest route is the

   "reverse chain rule with an undetermined polynomial coefficient" method: guess

   the shape of the antiderivative with unknown coefficients, differentiate, and

   match coefficients of like powers of $x$ to solve for them.

   Step-by-Step Solution

   1. Guess $f(x)=(ax^3+bx)\,(2x^4+3x^2+6)^{3/2}$.
   2. Differentiate (product + chain rule), then factor out $(2x^4+3x^2+6)^{1/2}$: $f'(x)=(2x^4+3x^2+6)^{1/2}\Big[(3ax^2+b)(2x^4+3x^2+6)+(ax^3+bx)(12x^3+9x)\Big]$.
   3. Expand the bracket: it collects to $18a\,x^6+(18a+14b)x^4+(18a+12b)x^2+6b$.
   4. Match this to the target $x^6+x^4+x^2$ (constant term $0$): $6b=0\Rightarrow b=0$; then $18a=1\Rightarrow a=\dfrac1{18}$.
   5. Check remaining coefficients with $a=1/18,\ b=0$: $18a+14b=1$ ✓ (matches $x^4$ coefficient $1$), $18a+12b=1$ ✓ (matches $x^2$ coefficient $1$). All consistent.
   6. So $f(x)=\dfrac{x^3}{18}(2x^4+3x^2+6)^{3/2}$.
   7. At $x=3$: $2(3)^4+3(3)^2+6=162+27+6=195$, and $x^3=27$.
   8. $f(3)=\dfrac{27}{18}(195)^{3/2}=\dfrac32(195)^{3/2}$.

   Common Mistakes

   • Guessing the wrong power on the ansatz's radical factor (e.g. using $(\cdot)^{1/2}$ instead of $(\cdot)^{3/2}$) — the chain rule from a $3/2$ power is exactly what produces both an $x^6$ and lower-power terms needed to match all three terms in the integrand.
   • Arithmetic slip evaluating $2\cdot3^4=162$ (not $2\cdot81=182$ or similar) — worth recomputing $3^4=81$ carefully.

   ✓Final answer

   The correct option is (B) — $\dfrac32(195)^{3/2}$.

   ANSWER: B

5. AP EAPCET 2022Set eng-2022-07-06-FN1 markMCQ
   Q.$\displaystyle\int \dfrac{1}{\left(\sin x + \cos x + \sqrt{2}\sqrt{\sin 2x}\right)^2}\,dx =$ (A) $\dfrac{-(1+3\sqrt{\tan x})}{(3+\tan^2 x)^3} + C$ (B) $\dfrac{-(1+3\sqrt{\tan x})}{3(1+\sqrt{\tan x})^3} + C$ (C) $\dfrac{-(1+\sqrt{\tan x})}{3(1+3\sqrt{\tan x})^2} + C$ (D) $\dfrac{1}{(1+3\sqrt{\tan x})^3} + C$

   ›Reveal solutionSolution

   Recognising the denominator as $(\sqrt{\sin x}+\sqrt{\cos x})^4$ and substituting $u=\sqrt{\tan x}$ reduces this to a rational integral, giving $-\dfrac{1+3\sqrt{\tan x}}{3(1+\sqrt{\tan x})^3}+C$.

   Concept and Intuition

   The key algebraic identity here is $(\sqrt{\sin x}+\sqrt{\cos x})^2 = \sin x + \cos x + 2\sqrt{\sin x\cos x} = \sin x+\cos x+\sqrt{2\sin 2x}$ (since $2\sqrt{\sin x\cos x}=\sqrt{4\sin x\cos x}=\sqrt{2\sin2x}$). That matches the given denominator's base exactly, turning a scary-looking radical expression into a clean fourth power.

   Step-by-Step Solution

   1. Verify $(\sqrt{\sin x}+\sqrt{\cos x})^2 = \sin x+\cos x+2\sqrt{\sin x\cos x} = \sin x+\cos x+\sqrt{2\sin2x}$, matching $\sin x+\cos x+\sqrt2\sqrt{\sin2x}$.
   2. So the denominator is $(\sqrt{\sin x}+\sqrt{\cos x})^4$.
   3. Factor out $\sqrt{\cos x}$: $\sqrt{\sin x}+\sqrt{\cos x} = \sqrt{\cos x}(\sqrt{\tan x}+1)$, so the denominator $=\cos^2x(1+\sqrt{\tan x})^4$.
   4. Integral becomes $\displaystyle\int \dfrac{\sec^2x\,dx}{(1+\sqrt{\tan x})^4}$. Let $t=\tan x$, $dt=\sec^2x\,dx$: $\displaystyle\int \dfrac{dt}{(1+\sqrt t)^4}$.
   5. Let $u=\sqrt t$, $t=u^2$, $dt=2u\,du$: $\displaystyle\int \dfrac{2u\,du}{(1+u)^4}$.
   6. Write $2u = 2(1+u)-2$: $\displaystyle\int\left[\dfrac{2}{(1+u)^3}-\dfrac{2}{(1+u)^4}\right]du = -\dfrac{1}{(1+u)^2}+\dfrac{2}{3(1+u)^3}+C$.
   7. Combine over a common denominator: $\dfrac{-3(1+u)+2}{3(1+u)^3} = \dfrac{-1-3u}{3(1+u)^3} = -\dfrac{1+3u}{3(1+u)^3}$.
   8. Substitute back $u=\sqrt{\tan x}$: result $= -\dfrac{1+3\sqrt{\tan x}}{3(1+\sqrt{\tan x})^3}+C$.

   Common Mistakes

   • Not spotting the perfect-square identity for the denominator and attempting brute-force substitution, which becomes intractable.
   • Errors combining fractions with different powers of $(1+u)$ in the final simplification step.

   ✓Final answer

   The correct option is (B) — $\dfrac{-(1+3\sqrt{\tan x})}{3(1+\sqrt{\tan x})^3} + C$.

   ANSWER: B

6. AP EAPCET 2022Set eng-2022-07-07-AN1 markMCQ
   Q.$\displaystyle\int \sqrt{x+\sqrt{x^2+2}}\,dx =$ (A) $\dfrac{3}{2}\left(x+\sqrt{x+2}\right)^{3/2} - 2\left(x+\sqrt{x^2+2}\right)^{1/4} + C$ (B) $\dfrac{1}{3}\left(x+\sqrt{x^2+2}\right)^{3/2} - 2\left(x+\sqrt{x^2+2}\right)^{1/4} + C$ (C) $\left(x+\sqrt{x^2+2}\right)^{-3/2} - 2\left(x+\sqrt{x^2+2}\right)^{-1/2} + C$ (D) $\dfrac{\left(x+\sqrt{x^2+2}\right)^2 - 6}{3\sqrt{x+\sqrt{x^2+2}}} + C$

   ›Reveal solutionSolution

   The substitution $t=x+\sqrt{x^2+2}$ rationalises the nested radical; the resulting antiderivative, written as a single fraction, matches option (D). Answer: option (D).

   Concept and Intuition

   Integrals containing $x+\sqrt{x^2+a^2}$ are a classic signal to substitute $t$ equal to that whole expression — it converts the awkward nested square root into simple powers of $t$, because $x$ and $\sqrt{x^2+a^2}$ can both be written as clean rational/linear functions of $t$.

   Step-by-Step Solution

   1. Let $t=x+\sqrt{x^2+2}$. Then $\sqrt{x^2+2}=t-x$; squaring, $x^2+2=t^2-2tx+x^2\Rightarrow 2=t^2-2tx\Rightarrow x=\dfrac{t^2-2}{2t}$.
   2. Then $\sqrt{x^2+2}=t-x=t-\dfrac{t^2-2}{2t}=\dfrac{2t^2-t^2+2}{2t}=\dfrac{t^2+2}{2t}$.
   3. Differentiate $t$ w.r.t. $x$: $\dfrac{dt}{dx}=1+\dfrac{x}{\sqrt{x^2+2}}=\dfrac{\sqrt{x^2+2}+x}{\sqrt{x^2+2}}=\dfrac{t}{\sqrt{x^2+2}}=\dfrac{t}{(t^2+2)/(2t)}=\dfrac{2t^2}{t^2+2}$, so $dx=\dfrac{t^2+2}{2t^2}dt$.
   4. Substitute into the integral: $\int\sqrt t\;dx=\int t^{1/2}\cdot\dfrac{t^2+2}{2t^2}dt=\dfrac12\int\left(t^{1/2}+2t^{-3/2}\right)dt$.
   5. Integrate: $\dfrac12\left[\dfrac23t^{3/2}-4t^{-1/2}\right]+C=\dfrac13t^{3/2}-2t^{-1/2}+C$.
   6. Combine over a common denominator $3\sqrt t$: $\dfrac{t^2-6}{3\sqrt t}+C$ (since $\dfrac{t^2}{3\sqrt t}=\dfrac13t^{3/2}$ and $\dfrac{-6}{3\sqrt t}=-2t^{-1/2}$), which is exactly option (D) with $t=x+\sqrt{x^2+2}$.

   Common Mistakes

   • Stopping at the split form $\dfrac13t^{3/2}-2t^{-1/2}+C$ and failing to recognise it as algebraically identical to the combined-fraction option (D) — always try simplifying a candidate option before ruling it out.
   • Sign or algebra slips solving for $x$ in terms of $t$.

   ✓Final answer

   The correct option is (D) — $\dfrac{\left(x+\sqrt{x^2+2}\right)^2 - 6}{3\sqrt{x+\sqrt{x^2+2}}} + C$.

   ANSWER: D

7. AP EAPCET 2023Set eng-2023-05-17-FN1 markMCQ
   Q.$\int(x^{3m}+x^{2m}+x^m)(2x^{2m}+3x^m+6)^{\frac{1}{m}}dx=$ (A) $\dfrac{1}{6(m+1)}\left(2x^{3m}+3x^{2m}+6x^m\right)^{\frac{m+1}{m}}+C$ (B) $\dfrac{1}{6(m+1)}\left(2x^{3m}+3x^{2m}+6x^m\right)^{\frac{m-1}{m}}+C$ (C) $\dfrac{1}{6(m+1)}\left(2x^{3m}+3x^{2m}+6\right)^{\frac{m+1}{m}}+C$ (D) $\dfrac{1}{6(m-1)}\left(2x^{3m}+mx^{2m}+6x^m\right)^{\frac{m-1}{m}}+C$

   ›Reveal solutionSolution

   Recognising that $2x^{3m}+3x^{2m}+6x^m$ equals $x^m$ times the bracket under the $1/m$-power root lets the whole integrand be rewritten as (a constant times) $g^{1/m}g'$ for $g=2x^{3m}+3x^{2m}+6x^m$ — a pure "power rule" integral.

   Concept and Intuition

   Whenever an integrand looks like $g(x)^{1/m}\cdot g'(x)$ (up to a constant factor), the antiderivative is immediately $\dfrac{g^{1/m+1}}{1/m+1}$. The main work here is algebraic: spotting that the "outside" factor $(x^{3m}+x^{2m}+x^m)$ is secretly related to the derivative of $g=2x^{3m}+3x^{2m}+6x^m$, and that the "inside" bracket $(2x^{2m}+3x^m+6)$ is just $g/x^m$.

   Step-by-Step Solution

   1. Let $g=2x^{3m}+3x^{2m}+6x^m$. Factor: $g=x^m(2x^{2m}+3x^m+6)$, so $2x^{2m}+3x^m+6=g/x^m$, and $(2x^{2m}+3x^m+6)^{1/m}=g^{1/m}/x$ (since $(g/x^m)^{1/m}=g^{1/m}/x$).
   2. Differentiate $g$: $g'=6mx^{3m-1}+6mx^{2m-1}+6mx^{m-1}=6mx^{m-1}(x^{2m}+x^m+1)$.
   3. Rewrite the integrand: $(x^{3m}+x^{2m}+x^m)(2x^{2m}+3x^m+6)^{1/m}=x^m(x^{2m}+x^m+1)\cdot\dfrac{g^{1/m}}x=x^{m-1}(x^{2m}+x^m+1)\,g^{1/m}$.
   4. From step 2, $x^{m-1}(x^{2m}+x^m+1)=\dfrac{g'}{6m}$. So the integrand equals $\dfrac{g'}{6m}g^{1/m}$.
   5. $\int\dfrac{g'}{6m}g^{1/m}\,dx=\dfrac1{6m}\int g^{1/m}\,dg=\dfrac1{6m}\cdot\dfrac{g^{1/m+1}}{1/m+1}+C=\dfrac1{6(m+1)}g^{(m+1)/m}+C$.
   6. Substituting back: $\dfrac1{6(m+1)}\left(2x^{3m}+3x^{2m}+6x^m\right)^{(m+1)/m}+C$.

   Common Mistakes

   • Mistaking the bracket raised to $1/m$ (which is $2x^{2m}+3x^m+6$, not $2x^{3m}+3x^{2m}+6x^m$) for $g$ itself — the two are related by a factor of $x^m$, which is exactly the subtlety that makes the problem work out.
   • Losing track of the exponent arithmetic $1/m+1=(m+1)/m$.

   ✓Final answer

   The correct option is (A) — $\dfrac1{6(m+1)}\left(2x^{3m}+3x^{2m}+6x^m\right)^{\frac{m+1}m}+C$.

   ANSWER: A

8. AP EAPCET 2026Set eng-2026-05-14-FN1 markMCQ
   Q.$\displaystyle\int \dfrac{dx}{(x^5+1)^{6/5}} =$ (A) $\dfrac{1}{\sqrt[5]{x^5+1}} + c$ (B) $\dfrac{\sqrt[5]{x^5+1}}{x} + c$ (C) $\dfrac{x}{\sqrt[5]{x^5+1}} + c$ (D) $\sqrt[5]{x^5+1} + c$

   ›Reveal solutionSolution

   Recognizing the integrand as the derivative of $\dfrac{x}{\sqrt[5]{x^5+1}}$ (verified by direct differentiation) gives the antiderivative immediately.

   Concept and Intuition

   For integrals of the form $\int\frac{dx}{(x^n+1)^{(n+1)/n}}$, a useful trick is to guess that the antiderivative looks like $\frac{x}{(x^n+1)^{1/n}}$ (a ratio designed to make the product-rule differentiation collapse nicely), and then verify by differentiating it — if it reproduces the integrand exactly, we're done. This is often faster than a substitution for this particular family.

   Step-by-Step Solution

   1. Guess the antiderivative $g(x) = \dfrac{x}{(x^5+1)^{1/5}} = x(x^5+1)^{-1/5}$.
   2. Differentiate using the product rule: $g'(x) = (x^5+1)^{-1/5} + x\cdot\left(-\dfrac15\right)(x^5+1)^{-6/5}\cdot5x^4$.
   3. Simplify the second term: $x\cdot\left(-\dfrac15\right)(5x^4)(x^5+1)^{-6/5} = -x^5(x^5+1)^{-6/5}$.
   4. So $g'(x) = (x^5+1)^{-1/5} - x^5(x^5+1)^{-6/5}$.
   5. Factor out $(x^5+1)^{-6/5}$: $g'(x) = (x^5+1)^{-6/5}\left[(x^5+1) - x^5\right] = (x^5+1)^{-6/5}\times 1 = (x^5+1)^{-6/5}$.
   6. This matches the integrand $\dfrac{1}{(x^5+1)^{6/5}}$ exactly.
   7. So $\displaystyle\int\dfrac{dx}{(x^5+1)^{6/5}} = \dfrac{x}{(x^5+1)^{1/5}}+c = \dfrac{x}{\sqrt[5]{x^5+1}}+c$.

   Common Mistakes

   • Forgetting the chain rule factor of $5x^4$ when differentiating $(x^5+1)^{-1/5}$-type expressions.
   • Choosing the wrong candidate antiderivative form (e.g. without the $x$ in the numerator), which would not reproduce the integrand upon differentiation.

   ✓Final answer

   The correct option is (C) — $\dfrac{x}{\sqrt[5]{x^5+1}} + c$.

   ANSWER: C

9. AP EAPCET 2022Set eng-2022-07-05-FN1 markMCQ
   Q.$\displaystyle\int \dfrac{dx}{(x-3)^{4/5}(x+1)^{6/5}} =$ (A) $\dfrac{5}{4}\sqrt[5]{\dfrac{x-3}{x+1}} + C$ (B) $\dfrac{5}{4}\left(\dfrac{x+1}{x-3}\right)^{1/5} + C$ (C) $\dfrac{1}{5}\left(\dfrac{x-3}{x+1}\right)^{1/5} + C$ (D) $\dfrac{5}{4}\left(\dfrac{x-3}{x+4}\right)^{4/5} + C$

   ›Reveal solutionSolution

   Splitting off $(x+1)^2$ turns the integrand into a pure power of $t=\frac{x-3}{x+1}$, giving $\frac54\left(\frac{x-3}{x+1}\right)^{1/5}+C$.

   Concept and Intuition

   When an integrand has the form $(x-a)^{p}(x-b)^{q}$ with $p+q$ an integer (here $\frac45+\frac65=2$), factoring out $(x-b)^{p+q}$ and substituting $t=\frac{x-a}{x-b}$ collapses the whole thing to a simple power of $t$ — a standard trick for these "unequal fractional exponent" integrals.

   Step-by-Step Solution

   1. $(x-3)^{4/5}(x+1)^{6/5} = (x+1)^2\left[\dfrac{x-3}{x+1}\right]^{4/5}$ (factoring out $(x+1)^{4/5+6/5}=(x+1)^2$).
   2. So the integrand is $(x+1)^{-2}\left[\dfrac{x-3}{x+1}\right]^{-4/5}$.
   3. Let $t=\dfrac{x-3}{x+1}$. Then $\dfrac{dt}{dx} = \dfrac{(x+1)-(x-3)}{(x+1)^2} = \dfrac{4}{(x+1)^2}$, so $(x+1)^{-2}dx = \dfrac{dt}{4}$.
   4. The integral becomes $\dfrac14\displaystyle\int t^{-4/5}\,dt = \dfrac14\cdot\dfrac{t^{1/5}}{1/5}+C = \dfrac54\,t^{1/5}+C$.
   5. Substitute back: $\dfrac54\left(\dfrac{x-3}{x+1}\right)^{1/5}+C = \dfrac54\sqrt[5]{\dfrac{x-3}{x+1}}+C$.
   6. (Verified by differentiating this result — it reproduces the original integrand exactly.)

   Common Mistakes

   • Splitting the powers the wrong way (factoring out $(x-3)^2$ instead of $(x+1)^2$), which inverts the fraction inside the fifth root.
   • Losing track of the constant $5/4$ when integrating $t^{-4/5}$.

   ✓Final answer

   The correct option is (A) — $\dfrac{5}{4}\sqrt[5]{\dfrac{x-3}{x+1}} + C$.

   ANSWER: A

10. AP EAPCET 2023Set eng-2023-05-18-FN1 markMCQ
    Q.If $\displaystyle\int \sqrt{x}(1-x^3)^{\frac{-1}{2}}dx=\dfrac{2}{3}g(f(x))+c$, then (A) $f(x)=\sqrt{x},\ g(x)=\sin^{-1}x$ (B) $f(x)=x^{3/2},\ g(x)=\sin^{-1}x$ (C) $f(x)=x^{3/2},\ g(x)=\cos^{-1}x$ (D) $f(x)=\sqrt{x},\ g(x)=\cos^{-1}x$

    ›Reveal solutionSolution

    A substitution $u=x^{3/2}$ turns the integral into the standard $\int du/\sqrt{1-u^2}$ form, giving $f(x)=x^{3/2}$ and $g=\sin^{-1}$.

    Concept and Intuition

    The presence of $\sqrt x\,dx$ alongside $x^3=(x^{3/2})^2$ inside a square root strongly signals the substitution $u=x^{3/2}$ (its derivative is proportional to $\sqrt x$, exactly what's needed to absorb the leftover $\sqrt x\,dx$). Once substituted, the integral collapses to the standard arcsine form.

    Step-by-Step Solution

    1. Let $u=x^{3/2}$. Then $du=\dfrac32 x^{1/2}\,dx=\dfrac32\sqrt x\,dx$, so $\sqrt x\,dx=\dfrac23\,du$.
    2. Also, $u^2=x^3$, so $1-x^3=1-u^2$.
    3. Substitute into the integral: $\displaystyle\int\sqrt x\,(1-x^3)^{-1/2}\,dx=\int\dfrac23\cdot\dfrac{du}{\sqrt{1-u^2}}=\dfrac23\int\dfrac{du}{\sqrt{1-u^2}}$.
    4. This is the standard form: $\displaystyle\int\dfrac{du}{\sqrt{1-u^2}}=\sin^{-1}u+c$.
    5. So the integral $=\dfrac23\sin^{-1}(u)+c=\dfrac23\sin^{-1}\left(x^{3/2}\right)+c$.
    6. Comparing with $\dfrac23 g(f(x))+c$: $f(x)=x^{3/2}$ and $g(x)=\sin^{-1}x$.

    Common Mistakes

    • Choosing $u=\sqrt x$ instead of $u=x^{3/2}$ — that substitution doesn't match the $x^3$ term inside the root cleanly.
    • Mixing up $\sin^{-1}$ with $\cos^{-1}$: since $\int du/\sqrt{1-u^2}=\sin^{-1}u+c$ (not $-\cos^{-1}u$, though that differs only by a constant, the problem's stated form fixes $g=\sin^{-1}$).

    ✓Final answer

    The correct option is (B) — $f(x)=x^{3/2}$, $g(x)=\sin^{-1}x$.

    ANSWER: B

11. AP EAPCET 2022Set eng-2022-07-08-FN1 markMCQ
    Q.$0 < x < 1$, $\int \dfrac{dx}{\sqrt{x^2 - x^5}} = \dfrac{1}{3}\log|f(x)| + C$, then $f(1/2) =$ (A) $\dfrac{\sqrt{8} - \sqrt{7}}{\sqrt{8} + \sqrt{7}}$ (B) $\dfrac{\sqrt{8} + \sqrt{7}}{\sqrt{8} - \sqrt{7}}$ (C) $2(\sqrt{8} - \sqrt{7})$ (D) $2(\sqrt{8} - \sqrt{7})^2$

    ›Reveal solutionSolution

    Substituting $t=x^3$ then $1-t=w^2$ integrates $\int dx/(x\sqrt{1-x^3})$ cleanly to $\tfrac13\log\left|\tfrac{1-\sqrt{1-x^3}}{1+\sqrt{1-x^3}}\right|$, and evaluating at $x=1/2$ gives $\dfrac{\sqrt8-\sqrt7}{\sqrt8+\sqrt7}$.

    Concept and Intuition

    The key simplification is $x^2-x^5=x^2(1-x^3)$, since $0<x<1$ makes $x>0$ so $\sqrt{x^2(1-x^3)}=x\sqrt{1-x^3}$. From there, the substitution $t=x^3$ turns the integral into the very standard form $\int\dfrac{dt}{t\sqrt{1-t}}$, solvable by a further substitution $1-t=w^2$.

    Step-by-Step Solution

    1. Rewrite: $\displaystyle I=\int\frac{dx}{\sqrt{x^2-x^5}}=\int\frac{dx}{x\sqrt{1-x^3}}$ (using $x>0$).
    2. Let $t=x^3\Rightarrow dt=3x^2dx\Rightarrow dx=\dfrac{dt}{3x^2}$. Then $I=\displaystyle\int\frac{dt}{3x^2\cdot x\sqrt{1-t}}=\int\frac{dt}{3x^3\sqrt{1-t}}=\frac13\int\frac{dt}{t\sqrt{1-t}}$ (since $x^3=t$).
    3. Let $1-t=w^2\Rightarrow t=1-w^2,\ dt=-2w\,dw$: $\displaystyle\int\frac{dt}{t\sqrt{1-t}}=\int\frac{-2w\,dw}{(1-w^2)w}=-2\int\frac{dw}{1-w^2}=-\log\left|\frac{1+w}{1-w}\right|=\log\left|\frac{1-w}{1+w}\right|$.
    4. So $I=\dfrac13\log\left|\dfrac{1-w}{1+w}\right|+C$ where $w=\sqrt{1-t}=\sqrt{1-x^3}$, i.e. $f(x)=\dfrac{1-\sqrt{1-x^3}}{1+\sqrt{1-x^3}}$.
    5. Verify by differentiating (chain rule through $w$) that this reproduces $\dfrac{1}{x\sqrt{1-x^3}}$ — confirmed.
    6. At $x=\tfrac12$: $1-x^3=1-\tfrac18=\tfrac78$, so $\sqrt{1-x^3}=\dfrac{\sqrt7}{\sqrt8}$.
    7. $f(1/2)=\dfrac{1-\sqrt7/\sqrt8}{1+\sqrt7/\sqrt8}=\dfrac{\sqrt8-\sqrt7}{\sqrt8+\sqrt7}$ (multiplying numerator and denominator by $\sqrt8$).

    Common Mistakes

    • Forgetting the extra factor of $x^2$ that arises from $dt=3x^2dx$ combined with the leftover $x$ from $x\sqrt{1-x^3}$ (easy to lose track of powers of $x$ during the $t=x^3$ substitution).
    • Sign error in the $1-w^2=(1-w)(1+w)$ partial-fraction step.

    ✓Final answer

    The correct option is (A) — $\dfrac{\sqrt{8} - \sqrt{7}}{\sqrt{8} + \sqrt{7}}$.

    ANSWER: A

12. AP EAPCET 2021Set eng-2021-08-20-FN1 markMCQ
    Q.If $\displaystyle\int \dfrac{(2x+1)^6}{(3x+2)^8}\, dx = P\left(\dfrac{2x+1}{3x+2}\right)^Q + R$, then $\dfrac{P}{Q} =$ _______ (A) $\dfrac{1}{7^2}$ (B) $\dfrac{1}{7}$ (C) $7^2$ (D) 7

    ›Reveal solutionSolution

    This tests a clever substitution $t=\frac{2x+1}{3x+2}$ that turns a messy rational integrand into a pure power of $t$. Answer: $\dfrac{P}{Q}=\dfrac{1}{7^2}$.

    Concept and Intuition

    When an integrand is a ratio of two linear-in-$x$ expressions raised to powers differing by exactly the right amount, substituting the ratio itself as a new variable can make $dx$ combine perfectly to leave a simple power of $t$.

    Step-by-Step Solution

    1. Let $t = \dfrac{2x+1}{3x+2}$.
    2. Differentiate: $\dfrac{dt}{dx} = \dfrac{2(3x+2)-(2x+1)\cdot3}{(3x+2)^2} = \dfrac{6x+4-6x-3}{(3x+2)^2} = \dfrac{1}{(3x+2)^2}$, so $dx = (3x+2)^2\,dt$.
    3. Substitute into the integral: $\dfrac{(2x+1)^6}{(3x+2)^8}\,dx = \dfrac{(2x+1)^6}{(3x+2)^8}\cdot(3x+2)^2\,dt = \dfrac{(2x+1)^6}{(3x+2)^6}\,dt = t^6\,dt$.
    4. So the integral $= \displaystyle\int t^6\,dt = \dfrac{t^7}{7}+c = \dfrac17\left(\dfrac{2x+1}{3x+2}\right)^7+c$.
    5. Comparing to $P\left(\frac{2x+1}{3x+2}\right)^Q+R$: $P=\dfrac17$, $Q=7$.
    6. $\dfrac PQ = \dfrac{1/7}{7} = \dfrac{1}{49} = \dfrac{1}{7^2}$.

    Common Mistakes

    • Trying to expand $(2x+1)^6$ and $(3x+2)^8$ directly by the binomial theorem instead of spotting the substitution — vastly more work and error-prone.

    ✓Final answer

    The correct option is (A) — $\dfrac{1}{7^2}$.

    ANSWER: A