Q.Evaluate the definite integral ∫01(xex+sin4πx)dx
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Integration by Parts
Integration by Parts
The idea: reverse the product rule
Some integrands are a product of two very different functions — xex, xcosx, logx, xsin−1x — where substitution gets you nowhere. Integration by parts is the tool for these. It comes straight from reversing the product rule for differentiation.
Starting from dxd(uv)=uv′+u′v and integrating both sides gives the working formula:
∫udxdvdx=uv−∫vdxdudx.
In words: integral of (first × derivative-of-second) = first × integral-of-second − integral of (derivative-of-first × integral-of-second).
Choosing u: the ILATE rule
The whole game is picking which factor is u (to differentiate) and which is dv (to integrate). Pick u by ILATE — the first type that appears:
- Inverse trig (sin−1x), Logarithmic (logx), Algebraic (x2), Trigonometric (sinx), Exponential (ex).
Whatever comes first in ILATE becomes u; the rest is dv. This makes the new integral ∫vdu simpler than the one you started with.
Worked idea
For ∫xexdx: algebraic before exponential, so u=x, dv=exdx. Then du=dx, v=ex:
∫xexdx=xex−∫exdx=xex−ex+C=ex(x−1)+C. …
The key idea is to split the integral into two simpler parts and evaluate each separately using standard antiderivatives.
Step 1: Split the integral
∫01xexdx+∫01sin4πxdx
Step 2: First integral — integration by parts
Let u=x, dv=exdx. Then du=dx, v=ex.
∫xexdx=xex−∫exdx=xex−ex+C
Evaluating from 0 to 1:
[(x−1)ex]01=(0⋅e1)−(−1⋅e0)=0+1=1
Step 3: Second integral — direct integration
∫sin4πxdx=−π4cos4πx+C
Evaluating from 0 to 1: …
We split the integral into two simpler integrals, evaluate each using standard techniques (integration by parts for xex, direct integration for sin4πx), and combine the results. The final value is 1+π4−22.
The key here is to break the problem into manageable pieces. A sum inside an integral can always be split into separate integrals — that's linearity, one of the most useful properties of definite integrals. Once we do that, each piece falls to a standard method.
- Split the integral using linearity:
∫01(xex+sin4πx)dx=∫01xexdx+∫01sin4πxdx
- Evaluate ∫01xexdx using integration by parts. The product x⋅ex is a classic case: let u=x and dv=exdx. Then du=dx and v=ex. Integration by parts gives:
∫udv=uv−∫vdu
So:
∫xexdx=xex−∫exdx=xex−ex+C=ex(x−1)+C
Now evaluate from 0 to 1:
[ex(x−1)]01=[e1(1−1)]−[e0(0−1)]=(e⋅0)−(1⋅(−1))=0+1=1
A quick check: the definite integral ∫01xexdx always equals 1 — a neat result worth remembering for speed.
- Evaluate ∫01sin4πxdx using a simple substitution. Let u=4πx, so du=4πdx, or dx=π4du. When x=0, u=0; when x=1, u=4π. The integral becomes:
∫01sin4πxdx=∫0π/4sinu⋅π4du=π4∫0π/4sinudu
The antiderivative of sinu is −cosu, so: …
Method: Split a sum, then choose the right tool for each piece
When the integrand is a sum of unrelated functions, use linearity to separate it, then match each piece to its own standard technique.
Steps
Step 1: Separate by linearity.
∫(u+v)dx=∫udx+∫vdx.
Step 2: For a product like xex, use integration by parts.
Pick u=x (the algebraic factor, so its derivative simplifies) and dv=exdx:
∫udv=uv−∫vdu. …
Common Mistakes
Mistake 1: Choosing u=ex instead of u=x in the by-parts for xex.
Why it's wrong: you want the algebraic factor x to differentiate away, so take u=x, dv=exdx; the other choice makes the integral harder. Correct approach: ∫xexdx=(x−1)ex, giving 1 on [0,1].
Mistake 2: Forgetting the π4 factor when integrating sin4πx. …
Showing the 12 most recent of 39 on this concept.
- AP EAPCET 2026Set eng-2026-05-12-FN1 markMCQQ.If ∫ex((2+x)3/22−x2−x2)dx=exf(x)+c, then the domain of f(x) is (A) (−∞,−2)∪(2,∞) (B) [−2,2] (C) (−2,2] (D) (−∞,−2]∪[2,∞)
›Reveal solutionSolution
This tests the standard trick ∫ex[f(x)+f′(x)]dx=exf(x)+c; here f(x)=(2−x)/(2+x) and its domain is (−2,2].
Concept and Intuition
Whenever an integral has the shape ex×(something) and the answer is stated as exf(x)+c, the 'something' must secretly be f(x)+f′(x) — this is because dxd[exf(x)]=ex[f(x)+f′(x)]. So the real task is pattern-matching the given rational expression to a function plus its derivative.
Step-by-Step Solution
- Guess a form built from the surds present: f(x)=2+x2−x=(2−x)1/2(2+x)−1/2.
- Differentiate using the product/chain rule: let u=(2−x)/(2+x); u′=(2+x)2−(2+x)−(2−x)=(2+x)2−4. Then f′(x)=21u−1/2u′=212−x2+x⋅(2+x)2−4=(2+x)3/2(2−x)1/2−2.
- Add: over the common denominator (2+x)3/2(2−x)1/2, the numerator of f(x) becomes (2−x)(2+x)=4−x2, and f′(x) contributes −2. Sum of numerators: 4−x2−2=2−x2.
- So f(x)+f′(x)=(2+x)3/2(2−x)1/22−x2, matching the given integrand exactly, confirming f(x)=2+x2−x. …
- AP EAPCET 2026Set eng-2026-05-13-FN1 markMCQQ.If f(x) is a twice differentiable function and f′(0)=0, then ∫0π/2(f(x)+f′′(x))cosxdx= (A) f(2π) (B) f′(2π) (C) 1 (D) 0
›Reveal solutionSolution
Two rounds of integration by parts on ∫0π/2f′′(x)cosxdx make the
∫f(x)cosxdx term reappear and cancel against the same term from the
original integral, leaving just f(π/2).
Concept and Intuition
When an integral mixes a function with its own second derivative against a
trigonometric weight, two rounds of integration by parts typically bring back a copy of
the original integral (since differentiating cosx twice returns −cosx,
picking up sign changes along the way) — so the two copies combine or cancel, leaving
only boundary terms.
Step-by-Step Solution
- Write the target as ∫0π/2f(x)cosxdx+∫0π/2f′′(x)cosxdx.
- For the second integral, integrate by parts with u=cosx, dv=f′′(x)dx so du=−sinxdx, v=f′(x): ∫0π/2f′′(x)cosxdx=[f′(x)cosx]0π/2+∫0π/2f′(x)sinxdx.
- Evaluate the boundary term: f′(π/2)cos(π/2)−f′(0)cos(0)=0−f′(0)⋅1=0 (using cos(π/2)=0 and the given f′(0)=0).
- So ∫0π/2f′′(x)cosxdx=∫0π/2f′(x)sinxdx.
- Integrate this by parts again, with u=sinx, dv=f′(x)dx so du=cosxdx, v=f(x): …
- AP EAPCET 2026Set eng-2026-05-14-AN1 markMCQQ.If ∫ex(x+1)3x3+3x2+4dx=exf(x)+c, then f(x)= (A) (x+1)2x2+2x−2 (B) (x+1)2x2+x−1 (C) (x+1)2x2−2x+2 (D) (x+1)2x2+2x−1
›Reveal solutionSolution
This is the classic ∫ex[f(x)+f′(x)]dx=exf(x)+c recognition problem; matching the rational integrand to g(x)+g′(x) for a guessed quadratic-over-(x+1)2 form pins down f(x)=(x+1)2x2+2x−2.
Concept and Intuition
Whenever an integral has the shape ∫ex⋅h(x)dx and the answer is claimed to be exf(x)+c, it must be that h(x)=f(x)+f′(x) (product rule run backwards). So instead of doing a hard partial-fraction integration of a rational function times ex, we can guess the shape of f(x) from the options (here, degree-2 over (x+1)2) and solve for its unknown coefficients algebraically.
Step-by-Step Solution
- We need f(x) with f(x)+f′(x)=(x+1)3x3+3x2+4. Try f(x)=(x+1)2x2+ax+b.
- Differentiate: f′(x)=(x+1)4(2x+a)(x+1)2−(x2+ax+b)⋅2(x+1)=(x+1)3(2x+a)(x+1)−2(x2+ax+b).
- Expand the numerator: (2x+a)(x+1)−2(x2+ax+b)=2x2+(2+a)x+a−2x2−2ax−2b=(2−a)x+(a−2b).
- So f′(x)=(x+1)3(2−a)x+(a−2b), while f(x)=(x+1)3(x2+ax+b)(x+1).
- Add: f(x)+f′(x)=(x+1)3(x2+ax+b)(x+1)+(2−a)x+(a−2b).
- Expand (x2+ax+b)(x+1)=x3+(1+a)x2+(a+b)x+b; adding the linear correction gives numerator x3+(1+a)x2+(b+2)x+(a−b). …
- AP EAPCET 2026Set eng-2026-05-18-FN1 markMCQQ.∫x2(logx)2dx= (A) 61x3[3(logx)2−3logx+4]+c (B) 271x3[9(logx)2−6logx+2]+c (C) 271x3[9(logx)2+6logx+2]+c (D) 91x3[6(logx)2−3logx+1]+c
›Reveal solutionSolution
Apply integration by parts twice (reduction formula style) on x2(logx)2; the result is 271x3[9(logx)2−6logx+2]+c.
Concept and Intuition
Each power of logx present costs one integration by parts with u=(logx)k, dv=xndx, reducing the power of the log by one each time. Two applications are needed here since (logx)2 appears.
Step-by-Step Solution
- First application (parts, u=(logx)2, dv=x2dx):
∫x2(logx)2dx=3x3(logx)2−32∫x2logxdx.
- Second application on ∫x2logxdx (u=logx, dv=x2dx):
∫x2logxdx=3x3logx−∫3x3⋅x1dx=3x3logx−9x3.
- Substitute back: ∫x2(logx)2dx=3x3(logx)2−32[3x3logx−9x3]=3x3(logx)2−92x3logx+272x3. …
- AP EAPCET 2026Set eng-2026-05-18-AN1 markMCQQ.If ∫ex(n1+tannx)secnxdx=n1(g(x)+k)=F(x) and F(0)=1, then k= (A) n (B) n+1 (C) n−1 (D) 1
›Reveal solutionSolution
Spot that the integrand is exactly the derivative of exsec(nx)/n (a product-rule construction), then use the initial condition F(0)=1 to pin down k.
Concept and Intuition
Many integrals of the form ex[p(x)+p′(x)] (or similar structured combinations) are designed to be exact derivatives of ex⋅(something), since dxd[exh(x)]=exh(x)+exh′(x). Recognizing h(x)=sec(nx)/n here (whose derivative is sec(nx)tan(nx)) collapses the whole integral instantly.
Step-by-Step Solution
- Try h(x)=nsec(nx). Then h′(x)=n1⋅nsec(nx)tan(nx)=sec(nx)tan(nx).
- So dxd[exh(x)]=exh(x)+exh′(x)=ex(nsec(nx)+sec(nx)tan(nx))=ex(n1+tan(nx))sec(nx) — exactly the given integrand.
- So ∫ex(n1+tannx)secnxdx=exh(x)+C=nexsec(nx)+C=n1(exsec(nx)+nC).
- Comparing to the given form n1(g(x)+k): g(x)=exsec(nx) and k=nC (a constant). …
- AP EAPCET 2026Set eng-2026-05-18-AN1 markMCQQ.If F(x)=∫x(logx)2dx and F(e)=4e2, then F(1)= (A) 0 (B) 41 (C) 21 (D) 3log(e2)
›Reveal solutionSolution
Integrating x(logx)2 twice by parts gives a closed form; matching F(e) pins the constant, then F(1)=1/4.
Concept and Intuition
∫x(logx)2dx is a repeated integration-by-parts problem: each application of parts trades one power of logx for a simpler integral, since dxd(logx)2=x2logx pairs nicely with ∫xdx=x2/2.
Step-by-Step Solution
- Let u=(logx)2, dv=xdx⇒du=x2logxdx, v=2x2.
F(x)=2x2(logx)2−∫xlogxdx
- For ∫xlogxdx, let u=logx, dv=xdx:
∫xlogxdx=2x2logx−4x2
- Substitute back:
F(x)=2x2(logx)2−2x2logx+4x2+C
- At x=e: loge=1, so
F(e)=2e2−2e2+4e2+C=4e2+C
Given F(e)=4e2, so C=0. …
- AP EAPCET 2026Set eng-2026-05-18-AN1 markMCQQ.If ∫e5xxndx=F(n,x)+c, then 5F(n,x)+nF(n−1,x)= (A) F′(n,x)+k (B) 51F′(n,x)+k (C) 5xF′(n,x)+k (D) F(n,x)x2F′(n,x)+k
›Reveal solutionSolution
Using the standard reduction formula for ∫eaxxndx and the fact that F′(n,x) is just the original integrand recovers 5F(n,x)+nF(n−1,x)=F′(n,x).
Concept and Intuition
F(n,x) is defined as an antiderivative, so by the Fundamental Theorem of Calculus its derivative is simply the integrand: F′(n,x)=e5xxn. Separately, integration by parts on ∫e5xxndx produces a reduction formula relating F(n,x) to F(n−1,x).
Step-by-Step Solution
- Integrate by parts with u=xn, dv=e5xdx⇒du=nxn−1dx, v=5e5x:
∫e5xxndx=5xne5x−5n∫e5xxn−1dx
- In terms of F: F(n,x)=5xne5x−5nF(n−1,x), so
5F(n,x)+nF(n−1,x)=xne5x
- But since F(n,x)+c=∫e5xxndx, differentiating both sides w.r.t. x gives F′(n,x)=e5xxn …
- AP EAPCET 2025Set eng-2025-05-21-FN1 markMCQQ.∫(logx)3x4dx= (A) x5[51(logx)3−253(logx)2+1256logx−6256]+c (B) x5[51(logx)3−252(logx)2+1256logx−12512]+c (C) x5[51(logx)3−254(logx)2−1259logx−1258]+c (D) x5[51(logx)3+253(logx)2−1256logx−1256]+c
›Reveal solutionSolution
Repeated integration by parts (equivalently, the standard reduction formula) on ∫x4(logx)3dx, reducing the power of logx one step at a time. Answer matches option (A).
Concept and Intuition
For ∫xn(logx)kdx, integrating by parts with u=(logx)k, dv=xndx gives the reduction
∫xn(logx)kdx=n+1xn+1(logx)k−n+1k∫xn(logx)k−1dx,
which is applied repeatedly until the power of logx drops to zero (a plain power integral).
Step-by-Step Solution
Here n=4, so the recursion factor is 5k at each step.
- Base (k=0): ∫x4dx=5x5.
- k=1: ∫x4logxdx=5x5logx−51∫x4dx=5x5logx−25x5.
- k=2:
∫x4(logx)2dx=5x5(logx)2−52∫x4logxdx=5x5(logx)2−52(5x5logx−25x5)
=5x5(logx)2−252x5logx+1252x5.
- k=3:
∫x4(logx)3dx=5x5(logx)3−53∫x4(logx)2dx
=5x5(logx)3−53(5x5(logx)2−252x5logx+1252x5) …
- AP EAPCET 2025Set eng-2025-05-21-AN1 markMCQQ.If ∫x2cos2xdx=61f(x)+g(x)sin2x+h(x)cos2x+c, then f(1)+g(2)+h(21)= (A) 0 (B) 2 (C) 1 (D) −1
›Reveal solutionSolution
Use cos2x=(1+cos2x)/2 to split the integral, then integrate x2cos2x by parts (twice) to get the sin2x and cos2x coefficient functions. Answer: f(1)+g(2)+h(1/2)=2.
Concept and Intuition
Squares of trig functions are best handled via the power-reduction (double-angle) identities, turning x2cos2x into a polynomial term plus a polynomial-times-cos2x term. The latter is a standard repeated integration-by-parts pattern (polynomial degree 2 needs two applications), producing terms in sin2x and cos2x with polynomial coefficients — exactly the structure the question sets up.
Step-by-Step Solution
- cos2x=21+cos2x, so x2cos2x=2x2+2x2cos2x.
- ∫2x2dx=6x3.
- For ∫x2cos2xdx, integrate by parts with u=x2,dv=cos2xdx:
∫x2cos2xdx=2x2sin2x−∫xsin2xdx.
- For ∫xsin2xdx, parts again with u=x,dv=sin2xdx:
∫xsin2xdx=−2xcos2x+∫2cos2xdx=−2xcos2x+4sin2x.
- Combine: ∫x2cos2xdx=2x2sin2x+2xcos2x−4sin2x.
- Halve (from step 1's factor 21): ∫2x2cos2xdx=4x2sin2x+4xcos2x−8sin2x. …
- AP EAPCET 2025Set eng-2025-05-23-FN1 markMCQQ.∫cos−1(1+x21−x2)dx= (A) 2[xtan−1x−log1+x2]+c (B) 2xtan−1x+log1+x2+c (C) xtan−1x+log1−x2+c (D) 2[tan−1x−log1+x2]+c
›Reveal solutionSolution
Recognising the standard identity cos−1(1+x21−x2)=2tan−1x turns this into a routine integration-by-parts problem.
Concept and Intuition
Substituting x=tanϕ turns 1+x21−x2 into cos2ϕ (the standard tangent half-angle relation), so cos−1(1+x21−x2)=2ϕ=2tan−1x (for the principal range where this holds).
Step-by-Step Solution
- cos−1(1+x21−x2)=2tan−1x.
- Integral becomes ∫2tan−1xdx.
- Integrate by parts with u=tan−1x, dv=dx: ∫tan−1xdx=xtan−1x−∫1+x2xdx.
- ∫1+x2xdx=21ln(1+x2)=log1+x2. …
- AP EAPCET 2025Set eng-2025-05-26-AN1 markMCQQ.∫(log2x)3dx= (A) x[(log2x)3−3(log2x)2+6(log2x)−6]+c (B) 4x[4(log2x)3−6(log2x)2+6(log2x)−3]+c (C) 2x[(log2x)3−3(log2x)2+3(log2x)−6]+c (D) x[(log2x)3−6(log2x)2+18(log2x)−54]+c
›Reveal solutionSolution
Because log(2x) differentiates exactly like logx, three rounds of integration by parts reproduce the classical (logx)3 antiderivative pattern.
Concept and Intuition
dxdlog(2x)=x1 — the constant factor 2 inside the log vanishes on differentiation. So treating u=log(2x) behaves exactly as u=logx would under repeated integration by parts with dv=dx.
Step-by-Step Solution
- Let t=log2x. Using ∫t3dx=xt3−3∫t2dx (parts: u=t3,dv=dx, du=3t2⋅x1dx, v=x).
- Similarly ∫t2dx=xt2−2∫tdx, and ∫tdx=xt−x.
- Back-substitute: ∫t2dx=xt2−2(xt−x)=xt2−2xt+2x.
- ∫t3dx=xt3−3(xt2−2xt+2x)=xt3−3xt2+6xt−6x. …
- AP EAPCET 2025Set eng-2025-05-26-FN1 markMCQQ.∫01xsin−1xdx= (A) 8π (B) 4π (C) 12π (D) 3π
›Reveal solutionSolution
Integration by parts on ∫01xsin−1xdx, with the resulting ∫x2/1−x2dx handled via a standard reduction, gives 8π.
Concept and Intuition
When the integrand is a product of a polynomial and an inverse trig function, integration by parts with u=sin−1x (so u′ is algebraic) and dv=xdx (easy to integrate) is the standard approach — it trades the inverse-trig factor for a simpler algebraic integral.
Step-by-Step Solution
- Let u=sin−1x, dv=xdx. Then du=1−x2dx, v=2x2.
- By parts: ∫xsin−1xdx=2x2sin−1x−∫21−x2x2dx.
- For ∫1−x2x2dx, write x2=1−(1−x2), so it equals ∫1−x2dx−∫1−x2dx=sin−1x−[2x1−x2+21sin−1x]=21sin−1x−2x1−x2.
- So ∫xsin−1xdx=2x2sin−1x−21[21sin−1x−2x1−x2]=2x2sin−1x−41sin−1x+4x1−x2. …
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