Q.Integrate the following function: (x3−1)1/3x5
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — U Substitution
U Substitution: The Reverse Chain Rule
The chain rule differentiates composite functions: the derivative of sin(x2) is cos(x2)⋅2x — differentiate the outer function, then multiply by the derivative of the inside. Integration asks the reverse: given cos(x2)⋅2x, find the original function. That's what u substitution does — it reverses the chain rule.
The Core Intuition
When an integral looks like "a function times the derivative of its inside," substitute the inside with u and the derivative of the inside with du. Consider:
∫2xcos(x2)dx
Here 2x is the derivative of x2, and x2 is the inside of cos(x2). Let u=x2, so du=2xdx:
∫cos(u)du=sin(u)+C=sin(x2)+C
Check: the derivative of sin(x2) is cos(x2)⋅2x.
The Precise Statement
∫f(g(x))⋅g′(x)dx=∫f(u)duwhere u=g(x),du=g′(x)dx
Valid provided g is differentiable and the resulting integral in u is simpler.
The Step-by-Step Method
- Identify a function g(x) whose derivative g′(x) also appears (possibly up to a constant factor).
- Set u=g(x), compute du=g′(x)dx.
- Rewrite the entire integral in u and du — every x and dx must be replaced.
- Integrate with respect to u.
- Substitute back u=g(x).
You cannot mix variables. If any x remains after substitution, you chose the wrong u (or must solve for x in terms of u — rare).
A Second Example (with a constant factor)
Evaluate ∫xx2+1dx. Let u=x2+1, so xdx=21du:
∫u⋅21du=21⋅32u3/2+C=31(x2+1)3/2+C
When Does It Work?
When the integrand is something times the derivative of something inside. Common patterns:
- x⋅f(x2) — derivative of x2 is 2x, so u=x2
- eg(x)⋅g′(x) — derivative of g(x) appears
- g(x)g′(x) — leads to log∣g(x)∣ …
Concept: U Substitution — we set u=x3−1 to simplify the power and then rewrite x5 in terms of u.
Let u=x3−1. Then du=3x2dx, so x2dx=3du.
Also x3=u+1, hence x5=x3⋅x2=(u+1)x2.
Substitute:
∫(x3−1)1/3x5dx=∫u1/3(u+1)⋅3du=31∫(u4/3+u1/3)du.
Integrate: …
With u=x3−1, ∫(x3−1)1/3x5dx=281(x3−1)4/3(4x3+3)+C.
1. Substitute. Let u=x3−1, so du=3x2dx, i.e. x2dx=31du, and x3=u+1.
2. Rewrite x5dx.
x5dx=x3⋅x2dx=(u+1)⋅31du.
3. Transform the integral.
∫(x3−1)1/3x5dx=31∫u1/3(u+1)du=31∫(u4/3+u1/3)du.
4. Integrate by the power rule.
31(73u7/3+43u4/3)+C=71u7/3+41u4/3+C.
5. Factor and back-substitute. …
Method: Substitute, then reuse the substitution to convert the extra powers
Use this when the power of x outside is higher than the derivative supplies — e.g. (x3−1)1/3x5: substitute u=x3−1, split x5=x3⋅x2, and re-express the leftover x3 as u+1.
Steps
Step 1: Substitute and peel off x2dx for du.
Let u=x3−1, so du=3x2dx. Write x5dx=x3⋅x2dx=x3⋅3du.
Step 2: Replace the remaining x3 using the substitution.
From u=x3−1 we get x3=u+1, so the integral becomes …
Common Mistakes
Mistake 1: Not splitting x5 into x3⋅x2.
Why it's wrong: only x2dx matches du=3x2dx; the remaining x3 must be handled separately. Correct approach: write x5dx=x3⋅x2dx and peel off x2dx for du.
Mistake 2: Forgetting to re-express the leftover x3 as u+1.
Why it's wrong: with u=x3−1, x3=u+1; leaving x3 un-substituted leaves the integral in two variables. Correct approach: replace x3 by u+1 to get 31∫u1/3(u+1)du. …
Showing the 12 most recent of 51 on this concept.
- AP EAPCET 2026Set eng-2026-05-14-FN1 markMCQQ.∫(x5+1)6/5dx= (A) 5x5+11+c (B) x5x5+1+c (C) 5x5+1x+c (D) 5x5+1+c
›Reveal solutionSolution
Recognizing the integrand as the derivative of 5x5+1x (verified by direct differentiation) gives the antiderivative immediately.
Concept and Intuition
For integrals of the form ∫(xn+1)(n+1)/ndx, a useful trick is to guess that the antiderivative looks like (xn+1)1/nx (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
- Guess the antiderivative g(x)=(x5+1)1/5x=x(x5+1)−1/5.
- Differentiate using the product rule: g′(x)=(x5+1)−1/5+x⋅(−51)(x5+1)−6/5⋅5x4.
- Simplify the second term: x⋅(−51)(5x4)(x5+1)−6/5=−x5(x5+1)−6/5.
- So g′(x)=(x5+1)−1/5−x5(x5+1)−6/5.
- Factor out (x5+1)−6/5: g′(x)=(x5+1)−6/5[(x5+1)−x5]=(x5+1)−6/5×1=(x5+1)−6/5. …
- AP EAPCET 2022Set eng-2022-07-05-FN1 markMCQQ.∫(x−3)4/5(x+1)6/5dx= (A) 455x+1x−3+C (B) 45(x−3x+1)1/5+C (C) 51(x+1x−3)1/5+C (D) 45(x+4x−3)4/5+C
›Reveal solutionSolution
Splitting off (x+1)2 turns the integrand into a pure power of t=x+1x−3, giving 45(x+1x−3)1/5+C.
Concept and Intuition
When an integrand has the form (x−a)p(x−b)q with p+q an integer (here 54+56=2), factoring out (x−b)p+q and substituting t=x−bx−a collapses the whole thing to a simple power of t — a standard trick for these "unequal fractional exponent" integrals.
Step-by-Step Solution
- (x−3)4/5(x+1)6/5=(x+1)2[x+1x−3]4/5 (factoring out (x+1)4/5+6/5=(x+1)2).
- So the integrand is (x+1)−2[x+1x−3]−4/5.
- Let t=x+1x−3. Then dxdt=(x+1)2(x+1)−(x−3)=(x+1)24, so (x+1)−2dx=4dt.
- The integral becomes 41∫t−4/5dt=41⋅1/5t1/5+C=45t1/5+C. …
- AP EAPCET 2024Set eng-2024-05-18-FN1 markMCQQ.∫x55x5+11dx= (A) 5x5+14+c (B) 4x4(x5+1)4/5+c (C) −4x4(x5+1)4/5+c (D) −4x5(x5+1)4/5+c
›Reveal solutionSolution
Rewriting the integrand to expose 1+x−5 as the natural substitution variable solves this cleanly; the answer is −4x4(x5+1)4/5+c.
Concept and Intuition
When an integral mixes a power of x with a root of a polynomial in x, factoring out the highest power of x from inside the root often converts the expression into a function of 1/x (or x−5 here), whose derivative is already present elsewhere in the integrand — a clean substitution.
Step-by-Step Solution
- (x5+1)−1/5=(x5(1+x−5))−1/5=x−1(1+x−5)−1/5.
- So the integrand x−5(x5+1)−1/5=x−6(1+x−5)−1/5.
- Let t=1+x−5, so dt=−5x−6dx⇒x−6dx=−5dt.
- Integral =∫t−1/5(−5dt)=−51⋅4/5t4/5+c=−41t4/5+c. …
- AP EAPCET 2026Set eng-2026-05-15-AN1 markMCQQ.If ∫x5e−4x3dx=481e−4x3f(x)+c, then f(x)= (A) −2x3−1 (B) −4x3−1 (C) −2x2+1 (D) 4x3+1
›Reveal solutionSolution
Substituting u=x3 converts the integral into a simple integration-by-parts problem ∫ue−4udu; matching the result to the given form yields f(x)=−4x3−1.
Concept and Intuition
The presence of x5 alongside e−4x3 is a strong hint to substitute u=x3, since then x2dx (part of du) combines with the remaining x3=u to leave a clean polynomial-times-exponential integral, solvable by the standard integration-by-parts reduction formula for ∫uekudu.
Step-by-Step Solution
- Let u=x3, so du=3x2dx⇒x2dx=3du.
- Rewrite x5e−4x3dx=x3⋅x2e−4x3dx=ue−4u⋅3du.
- So the integral becomes 31∫ue−4udu.
- Integrate by parts with first function u, second e−4u: ∫ue−4udu=u⋅(−4e−4u)−∫(−4e−4u)du=−4ue−4u−161e−4u. …
- AP EAPCET 2025Set eng-2025-05-22-FN1 markMCQQ.∫x2x4+x2+1x4−1dx= (A) x2x4+x2+1+c (B) xx4+x2+1+c (C) 2xx4+x2+1+c (D) x4x4+x2+1+c
›Reveal solutionSolution
Differentiating the candidate xx4+x2+1 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
- Try g(x)=xx4+x2+1=xN where N=x4+x2+1.
- N′=2x4+x2+14x3+2x=Nx(2x2+1).
- Quotient rule: g′(x)=x2N′x−N=x2Nx2(2x2+1)−N=Nx2x2(2x2+1)−N2.
- N2=x4+x2+1, so the numerator is x2(2x2+1)−(x4+x2+1)=2x4+x2−x4−x2−1=x4−1.
- So g′(x)=x2x4+x2+1x4−1 — exactly the given integrand. …
- AP EAPCET 2022Set eng-2022-07-08-FN1 markMCQQ.0<x<1, ∫x2−x5dx=31log∣f(x)∣+C, then f(1/2)= (A) 8+78−7 (B) 8−78+7 (C) 2(8−7) (D) 2(8−7)2
›Reveal solutionSolution
Substituting t=x3 then 1−t=w2 integrates ∫dx/(x1−x3) cleanly to 31log1+1−x31−1−x3, and evaluating at x=1/2 gives 8+78−7.
Concept and Intuition
The key simplification is x2−x5=x2(1−x3), since 0<x<1 makes x>0 so x2(1−x3)=x1−x3. From there, the substitution t=x3 turns the integral into the very standard form ∫t1−tdt, solvable by a further substitution 1−t=w2.
Step-by-Step Solution
- Rewrite: I=∫x2−x5dx=∫x1−x3dx (using x>0).
- Let t=x3⇒dt=3x2dx⇒dx=3x2dt. Then I=∫3x2⋅x1−tdt=∫3x31−tdt=31∫t1−tdt (since x3=t).
- Let 1−t=w2⇒t=1−w2, dt=−2wdw: ∫t1−tdt=∫(1−w2)w−2wdw=−2∫1−w2dw=−log1−w1+w=log1+w1−w.
- So I=31log1+w1−w+C where w=1−t=1−x3, i.e. f(x)=1+1−x31−1−x3.
- Verify by differentiating (chain rule through w) that this reproduces x1−x31 — confirmed. …
- AP EAPCET 2021Set eng-2021-08-23-AN1 markMCQQ.∫2/e1/ex(logx)1/31dx= (A) 23{1+(log(2)−1)2/3} (B) 1 (C) 23{1+(log(2)+1)3/2} (D) 23{1−(log(2)−1)2/3}
›Reveal solutionSolution
Substitute u=logx to turn the integral into ∫u−1/3du, then evaluate between the transformed limits u=log2−1 and u=−1.
Concept and Intuition
An integrand of the form x⋅g(logx)1 always calls for the substitution u=logx, since du=dx/x removes the x and 1/x entirely, leaving a pure power of u.
Step-by-Step Solution
- Let u=logx, so du=dx/x.
- Limits: at x=2/e, u=log(2/e)=log2−1. At x=1/e, u=log(1/e)=−1.
- The integral becomes ∫log2−1−1u−1/3du=[2/3u2/3]log2−1−1=23[u2/3]log2−1−1.
- Using the real cube root, (−1)2/3=((−1)1/3)2=(−1)2=1.
- So the value is 23[1−(log2−1)2/3].
Common Mistakes …
- AP EAPCET 2023Set eng-2023-05-18-FN1 markMCQQ.If ∫x(1−x3)2−1dx=32g(f(x))+c, then (A) f(x)=x, g(x)=sin−1x (B) f(x)=x3/2, g(x)=sin−1x (C) f(x)=x3/2, g(x)=cos−1x (D) f(x)=x, g(x)=cos−1x
›Reveal solutionSolution
A substitution u=x3/2 turns the integral into the standard ∫du/1−u2 form, giving f(x)=x3/2 and g=sin−1.
Concept and Intuition
The presence of xdx alongside x3=(x3/2)2 inside a square root strongly signals the substitution u=x3/2 (its derivative is proportional to x, exactly what's needed to absorb the leftover xdx). Once substituted, the integral collapses to the standard arcsine form.
Step-by-Step Solution
- Let u=x3/2. Then du=23x1/2dx=23xdx, so xdx=32du.
- Also, u2=x3, so 1−x3=1−u2.
- Substitute into the integral: ∫x(1−x3)−1/2dx=∫32⋅1−u2du=32∫1−u2du.
- This is the standard form: ∫1−u2du=sin−1u+c.
- So the integral =32sin−1(u)+c=32sin−1(x3/2)+c. …
- AP EAPCET 2023Set eng-2023-05-17-AN1 markMCQQ.If ∫1+x2x3dx=A(1+x2)3/2+B(1+x2)1/2+C, then A+B= (A) 2/3 (B) −2/3 (C) 1/3 (D) −1/3
›Reveal solutionSolution
The substitution u=1+x2 turns the integral into a simple power-rule computation, giving A=1/3 and B=−1, so A+B=−2/3.
Concept and Intuition
Whenever the integrand has an odd power of x alongside a function of x2 (here 1+x2), substituting u=1+x2 (so du=2xdx) converts the odd-power part into a polynomial in u, making the integral elementary.
Step-by-Step Solution
- Let u=1+x2, du=2xdx, and x2=u−1.
- x3dx=x2⋅xdx=(u−1)⋅2du.
- ∫1+x2x3dx=∫u(u−1)⋅2du=21∫(u1/2−u−1/2)du.
- =21(32u3/2−2u1/2)+C=31u3/2−u1/2+C. …
- AP EAPCET 2026Set eng-2026-05-14-FN1 markMCQQ.If ∫(x+5)x−5dx=152x−5f(x)+c, then f(6)= (A) 5 (B) 20 (C) 100 (D) 53
›Reveal solutionSolution
Substituting u=x−5 turns the integral into a simple power-rule computation; matching it to the given form and evaluating f at x=6 gives 53.
Concept and Intuition
An integrand with x−a multiplying a linear expression in x is best handled by substituting u=x−a, which converts everything into pure powers of u that integrate directly via the power rule. After integrating, we factor the result to match the given answer template and read off f(x).
Step-by-Step Solution
- Let u=x−5, so x=u+5, and x+5=u+10. Also dx=du.
- The integral becomes ∫(u+10)udu=∫(u3/2+10u1/2)du.
- Integrate term by term: ∫u3/2du=52u5/2, and ∫10u1/2du=10×32u3/2=320u3/2.
- So the integral =52u5/2+320u3/2+c.
- Factor out 152u3/2 (the common factor, chosen to match the given form's 152): 52u5/2=152u3/2(3u) and 320u3/2=152u3/2(50). So the integral =152u3/2(3u+50)+c=152u1/2⋅u(3u+50)+c. …
- AP EAPCET 2022Set eng-2022-07-06-AN1 markMCQQ.∫(sin2x+sin−3xcos5x)3cos4xdx= (A) 51(1+cot5x)−2+C (B) 101(1+cot2x)−5+C (C) 101(1+cot5x)−2+C (D) 51(1+cot5x)−5+C
›Reveal solutionSolution
Factoring sin2x out of the denominator turns it into sin2x(1+cot5x), and the substitution t=1+cot5x makes the whole integral a simple power-rule integration, giving 101(1+cot5x)−2+C.
Concept and Intuition
Integrals with mixed powers of sinx and cosx in odd/negative combinations often simplify beautifully once you factor out a common power to expose a (1+cotnx) or (1+tannx) structure — this is exactly the kind of expression whose derivative (via chain rule) reproduces cotn−1xcsc2x, matching what's left over in the integrand.
Step-by-Step Solution
- Denominator: sin2x+sin−3xcos5x. Factor out sin2x: =sin2x[1+sin5xcos5x]=sin2x(1+cot5x).
- So the full denominator cubed: [sin2x(1+cot5x)]3=sin6x(1+cot5x)3.
- Integrand: sin6x(1+cot5x)3cos4x=sin4xcos4x⋅sin2x1⋅(1+cot5x)−3=cot4xcsc2x(1+cot5x)−3.
- Substitute t=1+cot5x. Then dxdt=5cot4x⋅(−csc2x)=−5cot4xcsc2x, so cot4xcsc2xdx=−5dt. …
- AP EAPCET 2025Set eng-2025-05-23-AN1 markMCQQ.If ∫(x6+x4+x2)2x4+3x2+6dx=f(x)+c, then f(3)= (A) 23(95)3/2 (B) 23(195)3/2 (C) 23(265)3/2 (D) 23(175)3/2
›Reveal solutionSolution
Guess the antiderivative in the form (ax3+bx)(2x4+3x2+6)3/2, match
coefficients by differentiating, solve for a,b, then evaluate at x=3 to get
f(3)=23(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
(poly)⋅(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
- Guess f(x)=(ax3+bx)(2x4+3x2+6)3/2.
- Differentiate (product + chain rule), then factor out (2x4+3x2+6)1/2: f′(x)=(2x4+3x2+6)1/2[(3ax2+b)(2x4+3x2+6)+(ax3+bx)(12x3+9x)].
- Expand the bracket: it collects to 18ax6+(18a+14b)x4+(18a+12b)x2+6b.
- Match this to the target x6+x4+x2 (constant term 0): 6b=0⇒b=0; then 18a=1⇒a=181.
- Check remaining coefficients with a=1/18, b=0: 18a+14b=1 ✓ (matches x4 coefficient 1), 18a+12b=1 ✓ (matches x2 coefficient 1). All consistent.
- So f(x)=18x3(2x4+3x2+6)3/2. …
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