Q.Integrate the following function: x2−1x−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)∣ …
Split the fraction so each piece is a standard form:
x2−1x−1=x2−1x−x2−11.
First term. Let u=x2−1, so du=2xdx:
∫x2−1xdx=21∫u−1/2du=u=x2−1.
Second term is the standard result ∫x2−1dx=logx+x2−1. …
Split into x2−1x−x2−11; the first is a u-substitution, the second a standard form. Result: x2−1−logx+x2−1+C.
The idea
The numerator x−1 is two pieces bundled together. The x piece is (up to a factor of 2) exactly the derivative of x2−1 sitting under the root — a textbook cue for u-substitution. The −1 piece leaves x2−11, a standard integral. So split first, then handle each part.
x2−1x−1=x2−1x−x2−11.
Step 1 — the first term by substitution
Let u=x2−1, so du=2xdx, i.e. xdx=21du:
∫x2−1xdx=21∫udu=21⋅2u=x2−1.
Check: dxdx2−1=x2−1x. Correct.
Step 2 — the second term is standard
∫x2−1dx=logx+x2−1+C. …
Method: Split a fraction into a "derivative-of-radical" part plus a standard form
For x2−1x−1, separate the numerator so one piece matches the derivative of the radical (integrates to the radical itself) and the other is a standard reciprocal-radical form.
Steps
Step 1: Split the numerator.
x2−1x−1=x2−1x−x2−11
Step 2: Integrate the first piece by substitution.
For x2−1x, let u=x2−1, du=2xdx, giving ∫x2−1xdx=x2−1.
Step 3: Integrate the second piece with a standard form. …
Common Mistakes
Mistake 1: Trying a single substitution for the whole x2−1x−1.
Why it's wrong: the numerator mixes an x (whose derivative-of-radical structure fits) with a constant −1 (which does not), so one substitution cannot handle both. Correct approach: split into x2−1x−x2−11 and integrate each part.
Mistake 2: Using the wrong standard form for x2−11. …
Showing the 12 most recent of 51 on this concept.
- AP EAPCET 2025Set eng-2025-05-22-FN1 markMCQQ.∫x2x4+x2+1x4−1dx= (A) x2x4+x2+1+c (B) xx4+x2+1+c (C) 2xx4+x2+1+c (D) x4x4+x2+1+c
›Reveal solutionSolution
Differentiating the candidate xx4+x2+1 reproduces the given integrand exactly, confirming it as the antiderivative.
Concept and Intuition
When an integrand looks like it could come from a quotient rule (a square root over a power of x), it is often faster to differentiate a plausible candidate of that shape and check, rather than search for a substitution from scratch.
Step-by-Step Solution
- Try g(x)=xx4+x2+1=xN where N=x4+x2+1.
- N′=2x4+x2+14x3+2x=Nx(2x2+1).
- Quotient rule: g′(x)=x2N′x−N=x2Nx2(2x2+1)−N=Nx2x2(2x2+1)−N2.
- N2=x4+x2+1, so the numerator is x2(2x2+1)−(x4+x2+1)=2x4+x2−x4−x2−1=x4−1.
- So g′(x)=x2x4+x2+1x4−1 — exactly the given integrand. …
- AP EAPCET 2025Set eng-2025-05-27-FN1 markMCQQ.∫(1+x)x−x2dx= (A) −21−x1+x+c (B) −1+x1−x+c (C) −21+x1−x+c (D) 21−x1+x+c
›Reveal solutionSolution
Substituting t=x turns the surd-heavy integrand into ∫(1+t)3/2(1−t)1/22dt, whose antiderivative is exactly −21+t1−t.
Concept and Intuition
When an integrand mixes x and x−x2=x1−x, substituting t=x clears every square root of x at once, converting the whole thing into a rational-power integral in t that matches the derivative of 1+t1−t — a standard "recognise the derivative" pattern worth memorising for CET-style problems.
Step-by-Step Solution
- Write x−x2=x(1−x)=x1−x, so the integral is
I=∫(1+x)x1−xdx.
- Let t=x, so x=t2, dx=2tdt:
I=∫(1+t)⋅t⋅1−t22tdt=∫(1+t)(1−t)(1+t)2dt=∫(1+t)3/2(1−t)1/22dt.
- Let y=1+t1−t. Differentiating y2=1+t1−t: 2yy′=(1+t)2−(1+t)−(1−t)=(1+t)2−2 ⇒ y′=y(1+t)2−1=(1+t)3/2(1−t)1/2−1. …
- AP EAPCET 2025Set eng-2025-05-21-AN1 markMCQQ.If ∫(x−1)3/2(x−3)1/2dx=f(x)+c then f(−1)−f(0)= (A) −3 (B) −4 (C) −2 (D) −1
›Reveal solutionSolution
A classic "divide by (x−1)2 and substitute t=(x−3)/(x−1)" integral. It reduces to t, giving f(x)=(x−3)/(x−1), and then f(−1)−f(0)=−1.
Concept and Intuition
When an integrand has two linear factors under different fractional powers whose exponents sum to an integer (here 3/2+1/2=2), factor out (x−1)2 from the denominator and express the rest as a function of the ratio x−1x−3. This ratio then becomes a natural single substitution variable.
Step-by-Step Solution
- Write the denominator as
(x−1)3/2(x−3)1/2=(x−1)2⋅(x−1)1/2(x−3)1/2=(x−1)2x−1x−3.
- So the integral is ∫(x−1)2x−1x−3dx.
- Let t=x−1x−3=1−x−12. Then dxdt=(x−1)22, i.e. (x−1)2dx=2dt.
- The integral becomes ∫tdt/2=21⋅2t+c=t+c=x−1x−3+c. …
- AP EAPCET 2022Set eng-2022-07-08-FN1 markMCQQ.0<x<1, ∫x2−x5dx=31log∣f(x)∣+C, then f(1/2)= (A) 8+78−7 (B) 8−78+7 (C) 2(8−7) (D) 2(8−7)2
›Reveal solutionSolution
Substituting t=x3 then 1−t=w2 integrates ∫dx/(x1−x3) cleanly to 31log1+1−x31−1−x3, and evaluating at x=1/2 gives 8+78−7.
Concept and Intuition
The key simplification is x2−x5=x2(1−x3), since 0<x<1 makes x>0 so x2(1−x3)=x1−x3. From there, the substitution t=x3 turns the integral into the very standard form ∫t1−tdt, solvable by a further substitution 1−t=w2.
Step-by-Step Solution
- Rewrite: I=∫x2−x5dx=∫x1−x3dx (using x>0).
- Let t=x3⇒dt=3x2dx⇒dx=3x2dt. Then I=∫3x2⋅x1−tdt=∫3x31−tdt=31∫t1−tdt (since x3=t).
- Let 1−t=w2⇒t=1−w2, dt=−2wdw: ∫t1−tdt=∫(1−w2)w−2wdw=−2∫1−w2dw=−log1−w1+w=log1+w1−w.
- So I=31log1+w1−w+C where w=1−t=1−x3, i.e. f(x)=1+1−x31−1−x3.
- Verify by differentiating (chain rule through w) that this reproduces x1−x31 — confirmed. …
- AP EAPCET 2026Set eng-2026-05-13-AN1 markMCQQ.∫x2(x4+1)3/4dx= (A) (1+x41)3/4+c (B) (1+x61)1/2+c (C) −(1+x41)−1/4+c (D) −(1+x41)1/4+c
›Reveal solutionSolution
Pulling x4 out from under the radical and substituting t=1+x−4 reduces the integral to a simple power rule, giving −(1+1/x4)1/4+c.
Concept and Intuition
When the integrand has (xn+1)p, it often helps to factor out the highest power of x from inside the bracket so that a substitution like t=1+x−n produces a clean differential matching the rest of the integrand.
Step-by-Step Solution
- Write (x4+1)3/4=(x4(1+x41))3/4=x3(1+x41)3/4.
- So x2(x4+1)3/41=x2⋅x3(1+x41)3/41=x5(1+x41)3/41=x−5(1+x−4)−3/4.
- Let t=1+x−4. Then dt=−4x−5dx, so x−5dx=−4dt. …
- 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 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 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 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 2023Set eng-2023-05-18-FN1 markMCQQ.If ∫x(1−x3)2−1dx=32g(f(x))+c, then (A) f(x)=x, g(x)=sin−1x (B) f(x)=x3/2, g(x)=sin−1x (C) f(x)=x3/2, g(x)=cos−1x (D) f(x)=x, g(x)=cos−1x
›Reveal solutionSolution
A substitution u=x3/2 turns the integral into the standard ∫du/1−u2 form, giving f(x)=x3/2 and g=sin−1.
Concept and Intuition
The presence of xdx alongside x3=(x3/2)2 inside a square root strongly signals the substitution u=x3/2 (its derivative is proportional to x, exactly what's needed to absorb the leftover xdx). Once substituted, the integral collapses to the standard arcsine form.
Step-by-Step Solution
- Let u=x3/2. Then du=23x1/2dx=23xdx, so xdx=32du.
- Also, u2=x3, so 1−x3=1−u2.
- Substitute into the integral: ∫x(1−x3)−1/2dx=∫32⋅1−u2du=32∫1−u2du.
- This is the standard form: ∫1−u2du=sin−1u+c.
- So the integral =32sin−1(u)+c=32sin−1(x3/2)+c. …
- 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. …
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