Q.Integrate the following function: (x3−1)1/3x5
🔒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 →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 32 on this concept.
- KEAM 2024Set eng-2024-06074 marksMCQQ.∫x5ex3dx= (A) 3ex3(x3−1)+C (B) 5ex3(x5−1)+C (C) 4ex3(x4−1)+C (D) 3ex3(x5−1)+C (E) 3x3ex3+C
›Reveal solutionSolution
Substitute u=x3, then integrate ueu by parts.
Let u=x3, so du=3x2dx and x5dx=x3⋅x2dx=3udu. Thus
∫x5ex3dx=31∫ueudu.
By parts, ∫ueudu=ueu−eu=eu(u−1), so …
- KEAM 2026Set eng-2026-04184 marksMCQQ.∫(27x3(1−x3))32dx= (A) −43(1−x3)34+C (B) −53(1−x3)35+C (C) −39(1−x3)31+C (D) −49(1−x3)34+C (E) −59(1−x3)35+C
›Reveal solutionSolution
Simplify to 9x2(1−x3)2/3, then substitute u=1−x3 to obtain −59(1−x3)5/3+C.
Since (27x3(1−x3))2/3=272/3(x3)2/3(1−x3)2/3=9x2(1−x3)2/3, let u=1−x3, du=−3x2dx, so x2dx=−3du: …
- KEAM 2024Set eng-2024-06064 marksMCQQ.∫x4+3x2+1x2−1dx= (A) 31tan−1(3xx2+1)+C (B) tan−1(x2−1)+C (C) tan−1(x−x1)+C (D) 51tan−1(5xx2+1)+C (E) tan−1(x+x1)+C
›Reveal solutionSolution
The substitution u=x+x1 turns it into ∫u2+1du=tan−1(x+x1)+C.
Divide numerator and denominator by x2:
x4+3x2+1x2−1=x2+3+x211−x21. …
- KEAM 2024Set eng-2024-06054 marksMCQQ.∫x8(x71+1)2/3dx is equal to (A) 73(x71+1)2/3+C (B) −73(x71+1)2/3+C (C) −73(x71+1)1/3+C (D) 73(x71+1)1/3+C (E) 37(x71+1)2/3+C
›Reveal solutionSolution
The substitution u=x−7+1 reduces it to −71∫u−2/3du.
Let u=x71+1. Then du=−x87dx, so x8dx=−7du. The integral becomes …
- KEAM 2022Set eng-2022-P2-B14 marksMCQQ.∫x311−x21dx= (A) 6−1(1−x21)23+C (B) 31(1−x21)23+C (C) 3−1(1−x21)23+C (D) 34(1−x21)23+C (E) 3−4(1−x21)23+C
›Reveal solutionSolution
The integral equals 31(1−x21)3/2+C.
Concept and Intuition
The derivative of 1−x21 is x32, which matches the x31 factor outside the root, so a substitution linearizes the integral.
Step-by-Step Solution
- Let u=1−x21.
- du=x32dx⇒x3dx=2du.
- ∫x311−x21dx=∫u2du=21⋅3/2u3/2.
- =21⋅32u3/2=31u3/2=31(1−x21)3/2+C. …
- KEAM 2026Set eng-2026-04184 marksMCQQ.∫(2ex+5)310exdx is equal to (A) 2(2ex+5)25+C (B) (2ex+5)2−5+C (C) (2ex+5)2−10+C (D) 2(2ex+5)2−5+C (E) (2ex+5)25+C
›Reveal solutionSolution
Substitute u=2ex+5, du=2exdx, giving 5∫u−3du=−2(2ex+5)25+C.
Let u=2ex+5, so du=2exdx, i.e. exdx=2du. Then …
- KEAM 2026Set eng-2026-04174 marksMCQQ.∫xx+1dx= (A) 34(x+1)23+C (B) 32(x+1)23+C (C) 34(x+1)43+C (D) 31(x+1)23+C (E) 43(x+1)23+C
›Reveal solutionSolution
Substitute u=x+1.
With u=x+1, du=2x1dx, i.e. xdx=2du. Then …
- KEAM 2025Set eng-2025-04264 marksMCQQ.If ∫x7(x61+1)2/31dx=−21x61+11p+c, then p= (A) 32 (B) 3−1 (C) 31 (D) 3−2 (E) 61
›Reveal solutionSolution
Substitute u=x61+1; the result is −21u1/3, matched to the given form −21(1/u)p gives p=−1/3.
Let u=x61+1, so du=−x76dx, i.e. x7dx=−6du.
∫x7u−2/3dx=∫u−2/3(−6du)=−61⋅1/3u1/3=−21u1/3+c. …
- KEAM 2025Set eng-2025-04284 marksMCQQ.∫cos2/3xsin4/3xdx is (A) 3tan3x+C (B) 3tan1/3x+C (C) −3tan1/3x+C (D) −3tan−1/3x+C (E) 3tan−1/3x+C
›Reveal solutionSolution
Rewrite as sec2xtan−4/3xdx; sub t=tanx to get ∫t−4/3dt=−3t−1/3=−3tan−1/3x+C.
The integrand cos2/3xsin4/3x1 has denominator powers summing to 2, so factor out cos2x. Multiplying numerator and denominator by cos4/3x (equivalently dividing top and bottom by cos2x): …
- KEAM 2021Set eng-2021-P2-B14 marksMCQQ.∫x5e1−x6dx= (A) 61e1−x6+C (B) −e1−x6+C (C) 6−1e1−x6+C (D) 5x5e1−x6+C (E) 6x6e1−x6+C
›Reveal solutionSolution
∫x5e1−x6dx=−61e1−x6+C.
Concept and Intuition
The exponent's derivative dxd(1−x6)=−6x5 matches the algebraic factor x5, so a u-substitution collapses the integral.
Step-by-Step Solution
- Let u=1−x6, then du=−6x5dx, i.e. x5dx=−61du.
- Integral =∫eu(−61)du=−61eu+C. …
- KEAM 2025Set eng-2025-04234 marksMCQQ.∫1−x2sin−1xdx= (A) 21(sin−1x)2+C (B) −(sin−1x)1−x2+C (C) (sin−1x)1−x2+x+C (D) (sin−1x)1−x2−x+C (E) (sin−1x)2+C
›Reveal solutionSolution
Substituting u=sin^{-1}x turns the integral into u du = (1/2)(sin^{-1}x)^2 + C.
Concept and Intuition
The factor 1/sqrt(1-x^2) is exactly the derivative of sin^{-1}x, so the substitution u = sin^{-1}x collapses the integral.
Step-by-Step Solution
- Let u = sin^{-1}x, then du = dx/sqrt(1-x^2).
- The integral becomes integral of u du. …
- KEAM 2025Set eng-2025-04284 marksMCQQ.∫x(1−x)10dx= (A) 12(1−x)12−11(1−x)11+C (B) 12(1−x)12+11(1−x)11+C (C) 11(1−x)11−10(1−x)10+C (D) 12(1−x)12+11(1+x)11+C (E) 12(1−x)12−11(1+x)11+C
›Reveal solutionSolution
With u=1−x the integral becomes 12u12−11u11, i.e. 12(1−x)12−11(1−x)11+C.
Let u=1−x, x=1−u, dx=−du: …
🎓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.