Q.Integrate the following function: ∫x10+10x10x9+10xloge10dx equals (A) 10x−x10+C (B) 10x+x10+C (C) (10x−x10)−1+C (D) log(10x+x10)+C
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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 numerator is exactly the derivative of the denominator.
Let
u=x10+10x.
Then
dxdu=10x9+10xloge10,
so du=(10x9+10xloge10)dx.
The integral becomes …
The integrand is of the form f(x)f′(x), so the integral is log∣f(x)∣+C. Here f(x)=x10+10x, giving answer (D).
The key to this problem is recognising a pattern that appears again and again in integration: when you see a fraction where the numerator looks like the derivative of the denominator, you're looking at a natural logarithm result.
Let’s check that idea. If you have ∫f(x)f′(x)dx, the answer is log∣f(x)∣+C. Why? Because the derivative of logf(x) is f(x)f′(x) by the chain rule. So the whole game is: can we spot an f(x) whose derivative matches the numerator?
Here the denominator is x10+10x. Let’s differentiate it:
- The derivative of x10 is 10x9.
- The derivative of 10x is 10xloge10 (since dxdax=axloga).
So dxd(x10+10x)=10x9+10xloge10.
That is exactly the numerator. So we have:
∫x10+10x10x9+10xloge10dx=∫f(x)f′(x)dx
where f(x)=x10+10x.
Therefore:
∫f(x)f′(x)dx=log∣f(x)∣+C=log∣x10+10x∣+C
Since x10+10x is always positive for real x, we can drop the absolute value and write log(x10+10x)+C.
A common mistake is to confuse loge10 (a constant) with log10e or to forget that the derivative of 10x is 10xloge10, not 10x alone. Check the base carefully. …
Method: Numerator is the derivative of the denominator ⇒ logarithm
Use this whenever an integrand is a single fraction and the top looks like the derivative of the bottom. The antiderivative is then a natural logarithm — no formal substitution needed once you recognise it.
Steps
Step 1: Differentiate the denominator mentally.
Call the denominator f(x) and compute f′(x). Remember the non-polynomial derivatives that show up here: dxdax=axlogea and dxdxn=nxn−1.
Step 2: Check whether f′(x) equals the numerator.
If the numerator is exactly f′(x) (or a constant multiple of it), the integrand is in the form f(x)f′(x).
Step 3: Apply the standard result. …
Common Mistakes
Mistake 1: Choosing option (B), the antiderivative of the numerator alone.
Why it's wrong: 10x+x10 differentiates to the numerator, but this is a fraction f(x)f′(x), not just f′(x) — the denominator changes the antiderivative into a logarithm. Correct approach: apply ∫f(x)f′(x)dx=log∣f(x)∣+C.
Mistake 2: Using dxd10x=10x instead of 10xloge10. …
Showing the 12 most recent of 51 on this concept.
- AP EAPCET 2026Set eng-2026-05-15-FN1 markMCQQ.∫10+sin2xcosx−sinxdx= (A) 21log(10+sin2x)+c (B) 31log(10+sin2x)+c (C) 31Tan−1(3sinx+cosx)+c (D) 31Tan−1(10+sin2x)+c
›Reveal solutionSolution
The numerator cosx−sinx is exactly d(sinx+cosx), and the denominator rewrites in terms of u=sinx+cosx via sin2x=u2−1. That collapses the integral to a standard ∫du/(a2+u2) arctangent form. Answer: 31Tan−1(3sinx+cosx)+c.
Concept and Intuition
Whenever an integrand contains both sinx−cosx (or cosx−sinx) and sin2x, it is worth trying u=sinx+cosx (or sinx−cosx) as the substitution, because u2=1±sin2x links the two.
Step-by-Step Solution
- Let u=sinx+cosx. Then du=(cosx−sinx)dx — this is exactly the numerator times dx.
- Also u2=sin2x+cos2x+2sinxcosx=1+sin2x, so sin2x=u2−1.
- Denominator: 10+sin2x=10+u2−1=9+u2.
- The integral becomes ∫9+u2du=31Tan−1(3u)+c. …
- AP EAPCET 2023Set eng-2023-05-15-AN1 markMCQQ.∫4+5cosxdx= (A) −31log3−tan2x3+tan2x+C (B) 31log3−tan2x3+tan2x+C (C) −91log3+tan2x3−tan2x+C (D) 91log3+tan2x3−tan2x+C
›Reveal solutionSolution
The Weierstrass substitution t=tan(x/2) turns this into a standard ∫dt/(a2−t2) integral, giving option (B).
Concept and Intuition
For ∫a+bcosxdx the substitution t=tan(x/2) (so cosx=1+t21−t2, dx=1+t22dt) always converts the integral into a rational function of t alone.
Step-by-Step Solution
- cosx=1+t21−t2, dx=1+t22dt, with t=tan(x/2).
- 4+5cosx=4+5⋅1+t21−t2=1+t24(1+t2)+5(1−t2)=1+t29−t2.
- Integral becomes ∫(9−t2)/(1+t2)2dt/(1+t2)=∫9−t22dt.
- Using ∫a2−t2dt=2a1loga−ta+t+C with a=3: ∫9−t2dt=61log3−t3+t+C. …
- 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 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-2026-05-14-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-2024-05-22-FN1 markMCQQ.∫1+x8x3tan−1x4dx= (A) 8(tan−1(x4))2+c (B) 3(tan−1(x4))3+c (C) 4(tan−1(x4))2+c (D) 2(tan−1(x4))2+c
›Reveal solutionSolution
A double substitution (first u=x4, then v=tan−1u) turns this into a trivial ∫vdv. Answer: 8(tan−1x4)2+c.
Concept and Intuition
The presence of x3dx alongside x4 inside the arctan and x8=(x4)2 in the denominator is a strong signal to substitute u=x4 first. After that, the structure tan−1u⋅1+u2du is exactly of the form "function times its own derivative," solved by a second substitution.
Step-by-Step Solution
- Let u=x4, so du=4x3dx⇒x3dx=4du.
- The integral becomes ∫1+u2tan−1u⋅4du=41∫1+u2tan−1udu. …
- 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 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 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 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 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.∫(tan7x+tanx)dx= (A) 12tan2x(2tan4x−3tan2x+6)+c (B) 6tan2x−4tan5x+2tan4x+c (C) 6tan2x(tan4x+3tan2x+4)+c (D) 12tanx(tan4x−3tan2x+6)+c
›Reveal solutionSolution
Factoring tan7x+tanx using the sum-of-like-terms identity t7+t=t(t6+1)=t(t2+1)(t4−t2+1) exposes the sec2x needed for a clean t=tanx substitution. Answer: 12tan2x(2tan4x−3tan2x+6)+c.
Concept and Intuition
Whenever an integrand is built purely from powers of tanx together with an explicit or hidden sec2x, substituting t=tanx turns it into a polynomial integral — the key is recognizing that t6+1=(t2+1)(t4−t2+1) supplies exactly the sec2x=1+tan2x factor needed.
Step-by-Step Solution
- tan7x+tanx=tanx(tan6x+1)=tanx(tan2x+1)(tan4x−tan2x+1)=tanxsec2x(tan4x−tan2x+1).
- Let t=tanx, dt=sec2xdx. Integral becomes ∫t(t4−t2+1)dt=∫(t5−t3+t)dt.
- =6t6−4t4+2t2+c=6tan6x−4tan4x+2tan2x+c. …
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