Q.Integrate the following function: x(logx)m1, x>0,m=1
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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 — the derivative of logx appears in the denominator, so substitute u=logx.
Let u=logx. Then du=x1dx, and the integral becomes:
∫x(logx)m1dx=∫u−mdu
Integrate using the power rule (since m=1): …
The key idea is to use the substitution u=logx, which transforms the integral into a simple power of u. The result is 1−m(logx)1−m+C.
Why substitution works here
When you see a function like x(logx)m1, your first instinct should be to look for a composition — something inside something else. Here, the denominator has x multiplied by a power of logx. That x in the denominator is a strong hint: the derivative of logx is exactly x1. So if we set u=logx, then du=x1dx, and the whole integral collapses into something much simpler.
This is the classic pattern for u-substitution: you spot a function and its derivative (up to a constant) appearing together. Here, x1 is the derivative of logx, and (logx)m is the function itself raised to a power. That’s a perfect match.
A common mistake is to forget that m=1 is given. If m=1, the integral becomes ∫xlogx1dx, which gives log∣logx∣+C — a completely different form. The condition m=1 ensures we use the power rule, not the log rule.
Step-by-step solution
- Set up the substitution. Let u=logx. Then differentiate:
dxdu=x1⇒du=x1dx.
- Rewrite the integral in terms of u. The original integral is ∫x(logx)m1dx=∫(logx)m1⋅x1dx. …
Method: Substitute u=logx for a power of a logarithm over x
Use this when (logx) is raised to a power and divided by x, e.g. x(logx)m1: the x1 is precisely d(logx).
Steps
Step 1: Substitute the logarithm.
Let u=logx, so du=x1dx. The integral becomes ∫u−mdu.
Step 2: Apply the power rule (note m=1).
∫u−mdu=−m+1u−m+1+C=1−mu1−m+C. …
Common Mistakes
Mistake 1: Using the log rule instead of the power rule.
Why it's wrong: after u=logx the integral is ∫u−mdu; since m=1, the exponent −m=−1, so it is a power, not a logarithm. Correct approach: apply 1−mu1−m, reserving log∣u∣ only for m=1.
Mistake 2: Sign/arithmetic slip in the exponent 1−m. …
Showing the 12 most recent of 51 on this concept.
- AP EAPCET 2024Set eng-2024-05-23-FN1 markMCQQ.∫(logx)mxndx= (A) ∫tmentdt, t=ex (B) ∫tme(n+1)tdt, t=ex (C) ∫tme(n+1)tdt, x=et (D) ∫tmentdt, x=et
›Reveal solutionSolution
The substitution x=et (equivalently t=logx) converts a (logx)mxn integral into an exponential-times-power integral in t.
Concept and Intuition
When an integrand is built from logx and powers of x, setting x=et makes logx=t directly, and turns xndx into an exponential in t — a very standard substitution for this integral family.
Step-by-Step Solution
- Let x=et, so t=logx and dx=etdt.
- Then (logx)m=tm and xn=(et)n=ent.
- Substitute into the integral: ∫(logx)mxndx=∫tm⋅ent⋅etdt=∫tme(n+1)tdt. …
- AP EAPCET 2023Set eng-2023-05-17-FN1 markMCQQ.∫(x3m+x2m+xm)(2x2m+3xm+6)m1dx= (A) 6(m+1)1(2x3m+3x2m+6xm)mm+1+C (B) 6(m+1)1(2x3m+3x2m+6xm)mm−1+C (C) 6(m+1)1(2x3m+3x2m+6)mm+1+C (D) 6(m−1)1(2x3m+mx2m+6xm)mm−1+C
›Reveal solutionSolution
Recognising that 2x3m+3x2m+6xm equals xm times the bracket under the 1/m-power root lets the whole integrand be rewritten as (a constant times) g1/mg′ for g=2x3m+3x2m+6xm — a pure "power rule" integral.
Concept and Intuition
Whenever an integrand looks like g(x)1/m⋅g′(x) (up to a constant factor), the antiderivative is immediately 1/m+1g1/m+1. The main work here is algebraic: spotting that the "outside" factor (x3m+x2m+xm) is secretly related to the derivative of g=2x3m+3x2m+6xm, and that the "inside" bracket (2x2m+3xm+6) is just g/xm.
Step-by-Step Solution
- Let g=2x3m+3x2m+6xm. Factor: g=xm(2x2m+3xm+6), so 2x2m+3xm+6=g/xm, and (2x2m+3xm+6)1/m=g1/m/x (since (g/xm)1/m=g1/m/x).
- Differentiate g: g′=6mx3m−1+6mx2m−1+6mxm−1=6mxm−1(x2m+xm+1).
- Rewrite the integrand: (x3m+x2m+xm)(2x2m+3xm+6)1/m=xm(x2m+xm+1)⋅xg1/m=xm−1(x2m+xm+1)g1/m.
- From step 2, xm−1(x2m+xm+1)=6mg′. So the integrand equals 6mg′g1/m. …
- 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 2022Set eng-2022-07-06-FN1 markMCQQ.If ∫x2022(1+x2022)1/2022dx=nxn−(1+xm)n/m+C, then m−n= (A) 1 (B) 2 (C) 3 (D) 0
›Reveal solutionSolution
A standard ∫dx/[xk+1...] trick factoring xk out of the bracket gives m=2022, n=2021, hence m−n=1.
Concept and Intuition
For integrals of the form ∫xk(1+xk)1/kdx, the standard technique is to pull xk out from inside the bracket, turning it into (1+x−k), and then substitute u=1+x−k so that du naturally produces the x−(k+1)dx factor needed.
Step-by-Step Solution
- Write 1+x2022=x2022(1+x−2022), so (1+x2022)−1/2022=x−1(1+x−2022)−1/2022.
- The integrand becomes x−2022⋅x−1(1+x−2022)−1/2022=x−2023(1+x−2022)−1/2022.
- Let u=1+x−2022, so du=−2022x−2023dx⇒x−2023dx=−2022du.
- Integral =∫u−1/2022(−2022du)=−20221⋅2021/2022u2021/2022+C=−2021u2021/2022+C.
- Substitute back: u2021/2022=(1+x−2022)2021/2022=x2021(1+x2022)2021/2022. …
- AP EAPCET 2022Set eng-2022-07-07-AN1 markMCQQ.∫(1+x)2022dx= (A) (1+x)20212[20201+x−20211]+C (B) (1+x)20222[20201+x−2021x]+C (C) (1+x)2[2022(1+x)2022−2021(1+x)2021]+C (D) (1+x)21[(1+x)10101−(1+x)10111]+C
›Reveal solutionSolution
Substituting t=1+x turns the integral into a simple power-rule integral in t; back-substituting and factoring reproduces option (A)'s bracketed form.
Concept and Intuition
Whenever an integrand is a function purely of 1+x, the substitution t=1+x (so x=t−1, x=(t−1)2) turns the messy radical expression into a clean power of t, and the pieces of dx that are left over (2(t−1)dt) combine with the t−2022 factor to give a difference of two pure power terms — each integrable by the ordinary power rule.
Step-by-Step Solution
- Let t=1+x. Then x=t−1, x=(t−1)2, and dx=2(t−1)dt.
- The integral becomes ∫t20222(t−1)dt=2∫(t−2021−t−2022)dt.
- Integrate termwise: 2∫t−2021dt=−20202t−2020, and −2∫t−2022dt=−20212⋅(−1)t−2021⋅(−1), combining to 20212t−2021−20202t−2020. …
- AP EAPCET 2026Set eng-2026-05-12-FN1 markMCQQ.∫log2log3e2x−1e3x−3exdx= (A) log(32e) (B) log(34e) (C) 32e (D) 34e
›Reveal solutionSolution
A substitution t=ex turns this exponential integral into a rational one; the value works out to log(2e/3).
Concept and Intuition
Whenever an integral is built entirely from powers of ex, substituting t=ex converts it into an algebraic (rational function) integral, which is usually far easier to handle with partial fractions.
Step-by-Step Solution
- Let t=ex, so dt=exdx=tdx, i.e. dx=dt/t. When x=log2, t=2; when x=log3, t=3.
- Rewrite the integrand: e2x−1e3x−3ex=t2−1t3−3t. Multiplying by dx=dt/t gives t(t2−1)t3−3tdt=t2−1t2−3dt.
- So the integral becomes ∫23t2−1t2−3dt.
- Split: t2−1t2−3=t2−1(t2−1)−2=1−t2−12. …
- AP EAPCET 2023Set eng-2023-05-19-FN1 markMCQQ.If f(x)=(1+nxn)1/nx for n≥2, then ∫xn−2f(x)dx= (A) n(n−1)1(1+nxn)1−n1+C (B) n−11(1+nxn)1−n1+C (C) n(n−1)1(1+nxn)1+n1+C (D) n+11(1+nxn)1+n1+C
›Reveal solutionSolution
A direct substitution u=1+nxn turns the integral into a simple power rule.
Concept and Intuition
The integrand's power of x (namely xn−1) is exactly proportional to the derivative of u=1+nxn, which is the classic signal to substitute.
Step-by-Step Solution
- xn−2f(x)=xn−2⋅(1+nxn)1/nx=(1+nxn)1/nxn−1.
- Let u=1+nxn. Then du=n⋅nxn−1dx=n2xn−1dx, so xn−1dx=n2du.
- Integral becomes ∫u−1/n⋅n2du=n21⋅1−1/nu1−1/n+C.
- Simplify: n21⋅nn−11=n21⋅n−1n=n(n−1)1. …
- AP EAPCET 2024Set eng-2024-05-18-FN1 markMCQQ.∫log4log5e2x−5ex+6e2x+exdx= (A) log(964) (B) log(81256) (C) log(332) (D) log(27128)
›Reveal solutionSolution
Substituting t=ex turns the integral into a simple rational-function integral that evaluates to log(128/27).
Concept and Intuition
Whenever an integrand is built entirely out of ex (here e2x and ex), the substitution t=ex converts it into a rational function of t, which can then be handled by partial fractions — a standard technique for turning transcendental-looking integrals into algebraic ones.
Step-by-Step Solution
- Let t=ex, so dt=exdx=tdx, i.e. dx=tdt. When x=log4, t=4; when x=log5, t=5.
- Rewrite the integrand: e2x+ex=t2+t=t(t+1), and e2x−5ex+6=t2−5t+6=(t−2)(t−3).
- So ∫(t−2)(t−3)t(t+1)⋅tdt=∫45(t−2)(t−3)t+1dt.
- Partial fractions: (t−2)(t−3)t+1=t−2A+t−3B. At t=2: A=−13=−3. At t=3: B=14=4.
- So the integral is ∫45(t−2−3+t−34)dt=[−3log∣t−2∣+4log∣t−3∣]45. …
- 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 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 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 2024Set eng-2024-05-21-FN1 markMCQQ.If n≥2 is a natural number and 0<θ<2π, then ∫cosn+1θ(cosnθ−cosθ)1/nsinθdθ= (A) n−1n(cos(1−n)θ−1)2+c (B) (n+1)(1−n)n(cos(1−n)θ−1)1+n1+c (C) n−11(cos(n−1)θ−1)2+c (D) 1−n2n(1−cos(1−n)θ)(n+1)/n
›Reveal solutionSolution
Factor out cosnθ from inside the radical to isolate a clean power of cosθ, then substitute w=cos1−nθ to reduce the whole integral to ∫w1/ndw.
Concept and Intuition
The key move is factoring cosnθ−cosθ=cosnθ(1−cos1−nθ) so the n-th root pulls a clean cosθ outside, cancelling nicely against the cosn+1θ in the denominator and leaving a single power of w=cos1−nθ whose differential exactly matches sinθdθ/cosnθ in the integrand.
Step-by-Step Solution
- Factor: cosnθ−cosθ=cosnθ(1−cos1−nθ), so
(cosnθ−cosθ)1/n=cosθ(1−cos1−nθ)1/n.
- Divide by cosn+1θ:
cosn+1θ(cosnθ−cosθ)1/n=cosnθ(1−cos1−nθ)1/n.
- Let w=cos1−nθ. Then dθdw=(1−n)cos−nθ⋅(−sinθ)=(n−1)sinθcos−nθ, so cosnθsinθdθ=n−1dw.
- The whole integrand times dθ becomes (1−w)1/n⋅n−1dw — wait, more directly w1/n is the factor (1−cos1−nθ)1/n once we track 1−cos1−nθ as the base; carrying the substitution through consistently: …
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