Q.Integrate the function 1+x1−x
🔒You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.
🔒 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)∣ …
Rationalise by multiplying inside the root by 1−x1−x (for 0<x<1):
1+x1−x=1−x1−x=1−x1−1−xx.
First term: ∫1−xdx=−21−x. …
Rationalise the surd to 1−x1−x, split it, and integrate: the result is x−x2−21−x−sin−1x+C.
1. Kill the nested root
Multiply numerator and denominator inside the square root by 1−x (valid for 0<x<1, where 1−x≥0):
1+x1−x=(1+x)(1−x)(1−x)2=1−x1−x.
Split it into two manageable pieces:
1−x1−x=1−x1−1−xx.
2. First integral
∫1−xdx=−21−x.
3. Second integral
Put x=sin2θ, so dx=2sinθcosθdθ, x=sinθ, 1−x=cosθ:
∫1−xxdx=∫cosθsinθ2sinθcosθdθ=2∫sin2θdθ=∫(1−cos2θ)dθ=θ−sinθcosθ. …
Method: Rationalise a nested surd, then split and use a trig substitution
Use this for 1+x1−x-type integrands: multiply inside the root by the conjugate to remove the nesting, then handle each resulting piece separately.
Steps
Step 1: Rationalise inside the square root.
Multiply numerator and denominator inside the root by 1−x (valid where 1−x≥0), giving 1−x1−x.
Step 2: Split into manageable pieces.
1−x1−x=1−x1−1−xx. …
Common Mistakes
Mistake 1: Ignoring the domain when rationalising.
Why it's wrong: multiplying inside the root by 1−x needs 1−x≥0, i.e. 0<x<1. Correct approach: state the domain so the surd manipulation is valid.
Mistake 2: Mishandling the split 1−x1−x. …
Showing the 12 most recent of 51 on this concept.
- 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 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 2021Set eng-2021-08-25-AN1 markMCQQ.∫cosxdx= (A) 2xsinx+2cosx+c (B) 2xsinx+2sinx+c (C) 2xsinx−2cosx+c (D) xcosx−2sinx+c
›Reveal solutionSolution
Substitute t=x to turn the integral into a standard integration-by-parts problem. Answer: 2xsinx+2cosx+c.
Concept and Intuition
Whenever you see x trapped inside a trig or exponential function, substituting t=x converts it into a polynomial-times-trig integral solvable by parts.
Step-by-Step Solution
- Let t=x⇒x=t2, dx=2tdt.
- ∫cosxdx=∫cost⋅2tdt=2∫tcostdt.
- Integrate by parts: ∫tcostdt=tsint−∫sintdt=tsint+cost. …
- AP EAPCET 2022Set eng-2022-07-07-AN1 markMCQQ.∫x+x2+2dx= (A) 23(x+x+2)3/2−2(x+x2+2)1/4+C (B) 31(x+x2+2)3/2−2(x+x2+2)1/4+C (C) (x+x2+2)−3/2−2(x+x2+2)−1/2+C (D) 3x+x2+2(x+x2+2)2−6+C
›Reveal solutionSolution
The substitution t=x+x2+2 rationalises the nested radical; the resulting antiderivative, written as a single fraction, matches option (D). Answer: option (D).
Concept and Intuition
Integrals containing x+x2+a2 are a classic signal to substitute t equal to that whole expression — it converts the awkward nested square root into simple powers of t, because x and x2+a2 can both be written as clean rational/linear functions of t.
Step-by-Step Solution
- Let t=x+x2+2. Then x2+2=t−x; squaring, x2+2=t2−2tx+x2⇒2=t2−2tx⇒x=2tt2−2.
- Then x2+2=t−x=t−2tt2−2=2t2t2−t2+2=2tt2+2.
- Differentiate t w.r.t. x: dxdt=1+x2+2x=x2+2x2+2+x=x2+2t=(t2+2)/(2t)t=t2+22t2, so dx=2t2t2+2dt.
- Substitute into the integral: ∫tdx=∫t1/2⋅2t2t2+2dt=21∫(t1/2+2t−3/2)dt.
- Integrate: 21[32t3/2−4t−1/2]+C=31t3/2−2t−1/2+C. …
- 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 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 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 2023Set eng-2023-05-17-AN1 markMCQQ.If ∫1+x2x3dx=A(1+x2)3/2+B(1+x2)1/2+C, then A+B= (A) 2/3 (B) −2/3 (C) 1/3 (D) −1/3
›Reveal solutionSolution
The substitution u=1+x2 turns the integral into a simple power-rule computation, giving A=1/3 and B=−1, so A+B=−2/3.
Concept and Intuition
Whenever the integrand has an odd power of x alongside a function of x2 (here 1+x2), substituting u=1+x2 (so du=2xdx) converts the odd-power part into a polynomial in u, making the integral elementary.
Step-by-Step Solution
- Let u=1+x2, du=2xdx, and x2=u−1.
- x3dx=x2⋅xdx=(u−1)⋅2du.
- ∫1+x2x3dx=∫u(u−1)⋅2du=21∫(u1/2−u−1/2)du.
- =21(32u3/2−2u1/2)+C=31u3/2−u1/2+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 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 2024Set eng-2024-05-20-AN1 markMCQQ.∫sin3xcos(x−α)dx= (A) cosα1cotx+tanα+c (B) cosα1cotx−tanα+c (C) sinα−1cotx+tanα+c (D) cosα−2cotx+tanα+c
›Reveal solutionSolution
Expanding cos(x−α) and substituting u=cotx reduces this to a simple square-root integral; final answer is (D).
Concept and Intuition
The key move is expanding cos(x−α) and factoring out sin4x from inside the square root so that a substitution u=cotx (whose differential is −csc2xdx, conveniently matching what's left outside) linearizes the whole thing.
Step-by-Step Solution
- cos(x−α)=cosxcosα+sinxsinα.
- sin3xcos(x−α)=sin3xcosxcosα+sin4xsinα=sin4x(sinxcosxcosα+sinα)=sin4x(cotxcosα+sinα).
- So sin3xcos(x−α)=sin2xcotxcosα+sinα (taking sin2x>0 outside the root).
- The integral is ∫sin2xcosαcotx+sinαdx=∫cosαcotx+sinαcsc2xdx.
- Let u=cotx, du=−csc2xdx. Integral becomes −∫cosαu+sinαdu=−cosα2cosαu+sinα+c. …
🎓Unlock everything free for 14 days
- ✓Full step-by-step solutions
- ✓Concept-first explanations
- ✓Methods, shortcuts & mistakes
- ✓PYQ mapping + timed mock tests
Full access for 14 days. No credit card required.