Q.Integrate the following function: e2xsinx
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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 treat this as a product of two functions and apply integration by parts twice, then solve for the original integral.
Let I=∫e2xsinxdx.
Step 1: Choose u=sinx, dv=e2xdx. Then du=cosxdx, v=21e2x.
I=21e2xsinx−21∫e2xcosxdx
Step 2: Apply integration by parts again to ∫e2xcosxdx. Let u=cosx, dv=e2xdx, so du=−sinxdx, v=21e2x.
∫e2xcosxdx=21e2xcosx+21∫e2xsinxdx=21e2xcosx+21I
Step 3: Substitute back into the expression for I:
I=21e2xsinx−21(21e2xcosx+21I) …
The integral of e2xsinx is found using integration by parts twice, which creates a cyclic equation that we solve algebraically. The final result is 5e2x(2sinx−cosx)+C.
Why This Approach Works
When you see a product of an exponential and a trigonometric function, your first instinct might be to try substitution — but that won't help here because neither function is the derivative of the other in a simple way. The key insight is that integration by parts can reduce the complexity step by step, but because both e2x and sinx are "cyclic" under differentiation (they loop back to themselves after two derivatives), we end up with the original integral reappearing. That lets us treat it as an algebraic equation and solve for the unknown integral.
This "recurring integral" trick works for any pair of functions that are each other's derivatives up to a constant factor — like eaxsin(bx) or eaxcos(bx). You never need to memorize a formula; just set up the equation.
Step-by-Step Solution
-
Set up the integral and choose parts.
Let I=∫e2xsinxdx.
For integration by parts, we need u and dv. A good rule: pick u as the function that simplifies when differentiated. Here, both e2x and sinx are fine, but let's choose:
u=sinx, dv=e2xdx.
Then du=cosxdx, and v=∫e2xdx=21e2x.
-
Apply integration by parts the first time.
The formula ∫udv=uv−∫vdu gives:
I=sinx⋅21e2x−∫21e2xcosxdx=21e2xsinx−21∫e2xcosxdx.
- Now we need ∫e2xcosxdx — call it J. Apply integration by parts again to J. This time, let u=cosx, dv=e2xdx. Then du=−sinxdx, v=21e2x. So:
J=cosx⋅21e2x−∫21e2x(−sinx)dx=21e2xcosx+21∫e2xsinxdx.
- Notice the original integral I has reappeared. The last term is exactly 21I. So we have:
J=21e2xcosx+21I.
- Substitute J back into the expression for I. From step 2: I=21e2xsinx−21J. Replace J: I=21e2xsinx−21(21e2xcosx+21I). …
Method: Cyclic integration by parts (exponential times sine/cosine)
For eaxsinbx or eaxcosbx, two rounds of by parts reproduce the original integral, which you then solve algebraically.
Steps
Step 1: Call the integral I and integrate by parts once.
Let I=∫e2xsinxdx. Take u=sinx, dv=e2xdx (either choice works if kept consistent), producing an e2xcosx integral.
Step 2: Integrate by parts a second time, consistently.
Apply by parts to the new integral with the same type of choice. A term equal to a multiple of the original I reappears.
Step 3: Solve for I algebraically.
You reach a relation like I=(boundary terms)−kI. Collect the I terms: …
Common Mistakes
Mistake 1: Switching the by-parts choice between the two passes.
Why it's wrong: differentiating the exponential in one pass and integrating it in the next unravels the loop back to 0=0. Correct approach: keep the same role (always u= trig, or always u= exponential) both times.
Mistake 2: Panicking when the original integral reappears.
Why it's wrong: the reappearance is the whole mechanism, not a dead end. Correct approach: treat I as an unknown and solve the linear equation for it. …
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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