Q.Integrate the following function: (x2+1)(x−1)x
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Partial Fraction Decomposition
Partial Fraction Decomposition
Adding x−12+x+23 over a common denominator gives x2+x−25x+1. Partial fraction decomposition reverses this — it breaks one complicated rational function back into a sum of simple pieces. Those pieces are far easier to integrate: ∫x−12dx=2log∣x−1∣ is immediate, while the combined fraction is not.
When it applies
You need a proper rational function, degP<degQ. If the numerator's degree is equal or higher, first do polynomial long division. The denominator Q(x) must be factored into linear and/or irreducible quadratic factors.
The standard forms
For Q(x)P(x) with Q fully factored, each factor contributes a term:
- Distinct linear (ax+b) → ax+bA.
- Repeated linear (ax+b)n → ax+bA1+(ax+b)2A2+⋯+(ax+b)nAn.
- Irreducible quadratic (ax2+bx+c) → ax2+bx+cAx+B — a linear numerator, not just a constant.
The unknown constants are found from the resulting equations; the decomposition is unique, which is what lets us solve for them systematically.
Worked example
Decompose x2−3x+23x+5. Factor the denominator: (x−1)(x−2). Set
(x−1)(x−2)3x+5=x−1A+x−2B.
Clear denominators: 3x+5=A(x−2)+B(x−1). Substituting the roots, x=1 gives 8=−A so A=−8, and x=2 gives 11=B. Hence
x2−3x+23x+5=x−1−8+x−211.
With distinct linear factors, substitute each factor's root to knock out all but one term — much faster than equating coefficients. …
The factor x2+1 is irreducible, so it needs a linear numerator:
(x2+1)(x−1)x=x2+1Ax+B+x−1C.
Clearing, x=(Ax+B)(x−1)+C(x2+1). Matching coefficients:
A+C=0,−A+B=1,−B+C=0⇒A=−21, B=21, C=21.
Integrate: …
With the irreducible factor x2+1 carrying an Ax+B numerator, decompose and integrate to −41log(x2+1)+21tan−1x+21log∣x−1∣+C.
Setting up the form
An irreducible quadratic factor needs a linear numerator; a linear factor needs a constant:
(x2+1)(x−1)x=x2+1Ax+B+x−1C.
Step 1 — clear denominators and solve
x=(Ax+B)(x−1)+C(x2+1)=(A+C)x2+(B−A)x+(C−B).
Matching x2, x1, x0 against 0⋅x2+1⋅x+0:
A+C=0,B−A=1,C−B=0.
From the last, C=B; from the first, A=−C=−B; then B−A=2B=1⇒B=21, so A=−21, C=21.
Step 2 — split the quadratic piece
x2+1−21x+21=−21⋅x2+1x+21⋅x2+11.
Step 3 — integrate each term
- −21∫x2+1xdx=−41log(x2+1) (let u=x2+1). …
Method: Partial fractions with an irreducible quadratic factor
Use this for (irreducible quadratic)(linear)N(x), e.g. a factor x2+1 that has no real roots. An irreducible quadratic factor needs a linear numerator, not a constant.
Steps
Step 1: Assign numerators by factor type. A linear factor (x−r) gets a constant; an irreducible quadratic (x2+px+q) gets a linear numerator:
(x2+1)(x−r)N(x)=x2+1Ax+B+x−rC.
Step 2: Clear denominators and match all coefficients (x2, x1, x0) to solve for A,B,C (the cover-up trick only gives the constant C directly). …
Common Mistakes
Mistake 1: Giving the irreducible quadratic a constant numerator.
Why it's wrong: writing x2+1A instead of x2+1Ax+B has too few unknowns and cannot reproduce the original fraction. Correct approach: an irreducible quadratic factor always takes a linear numerator Ax+B.
Mistake 2: Forgetting the 21 when integrating x2+1x.
Why it's wrong: ∫x2+1xdx=21log(x2+1) (since d(x2+1)=2xdx), whereas ∫x2+11dx=tan−1x — mixing them scales the log term wrongly. Correct approach: split x2+1Ax+B into the x-part (log) and the constant-part (arctan) separately. …
Showing the 12 most recent of 63 on this concept.
- AP EAPCET 2025Set eng-2025-05-23-FN1 markMCQQ.∫x3−1x+1dx= (A) 31log(x2+x+1x+1)+c (B) 31log(x2+x+1(x−1)2)+c (C) 31log(x2+x+1x−1)+c (D) 31log(x2−x+1(x+1)2)+c
›Reveal solutionSolution
This is a rational-function integral solved by partial fractions after factoring x3−1; the result combines into a single log of x2+x+1(x−1)2.
Concept and Intuition
Factor the cubic denominator as difference of cubes, then split into a linear-factor term (giving a plain log) and an irreducible-quadratic term (giving a log plus, here, no arctangent term since the numerator works out to be an exact multiple of the quadratic's derivative).
Step-by-Step Solution
- x3−1=(x−1)(x2+x+1).
- Write (x−1)(x2+x+1)x+1=x−1A+x2+x+1Bx+C.
- x+1=A(x2+x+1)+(Bx+C)(x−1). At x=1: 2=3A⇒A=32.
- Matching x2: A+B=0⇒B=−32. Matching constants: A−C=1⇒C=−31.
- ∫x−12/3dx=32log∣x−1∣.
- ∫x2+x+1−32x−31dx=−31∫x2+x+12x+1dx=−31log(x2+x+1) (numerator is exactly the derivative of the denominator). …
- AP EAPCET 2023Set eng-2023-05-18-FN1 markMCQQ.∫(x2−1)(x2+1)x2dx= (A) 41logx−1x+1−21Tan−1x+c (B) 41logx+1x−1+21Tan−1x+c (C) 41logx+1x−1−21Tan−1x+c (D) 41logx−1x+1+21Tan−1x+c
›Reveal solutionSolution
Splitting x4−1x2 into a sum of x2−11 and x2+11 (halved) gives a standard log + arctan combination.
Concept and Intuition
Rather than doing full partial fractions with four unknowns, it's faster to notice x4−1=(x2−1)(x2+1) and that x2−11+x2+11=x4−1(x2+1)+(x2−1)=x4−12x2. This directly gives x4−1x2 as half that sum — a shortcut avoiding solving for four separate constants.
Step-by-Step Solution
- Write the denominator as x4−1=(x2−1)(x2+1).
- Observe: x2−11+x2+11=x4−12x2, so x4−1x2=21[x2−11+x2+11].
- Use the standard integrals: ∫x2−1dx=21logx+1x−1+c1 and ∫x2+1dx=tan−1x+c2.
- Combine: ∫x4−1x2dx=21[21logx+1x−1+tan−1x]+c=41logx+1x−1+21tan−1x+c.
Common Mistakes …
- AP EAPCET 2026Set eng-2026-05-13-FN1 markMCQQ.If (x2+1)2(x−1)x=x2+1Ax+B+(x2+1)2Cx+D+x−1E, then A+B−C+2D= (A) 21 (B) 1 (C) 23 (D) 2
›Reveal solutionSolution
This tests standard partial-fraction decomposition with a repeated irreducible quadratic factor, using a mix of "plug in a root" and "match coefficients" techniques. The final computed value is A+B−C+2D=1.
Concept and Intuition
When the denominator has an irreducible quadratic factor repeated twice, (x2+1)2, along with a simple linear factor (x−1), the partial fraction form needs a linear numerator (Ax+B, Cx+D) over each power of the quadratic, plus a constant (E) over the linear factor. The cleanest way to solve is: clear denominators, plug in the linear factor's root to isolate E instantly, then expand the rest and match coefficients of each power of x to get the remaining unknowns.
Step-by-Step Solution
- Clear denominators by multiplying both sides by (x2+1)2(x−1):
x=(Ax+B)(x2+1)(x−1)+(Cx+D)(x−1)+E(x2+1)2.
- Find E quickly: set x=1. The first two terms vanish (each has a factor of (x−1)), leaving 1=E(12+1)2=4E, so E=41.
- Expand the rest. First, (x2+1)(x−1)=x3−x2+x−1, so
(Ax+B)(x3−x2+x−1)=Ax4+(−A+B)x3+(A−B)x2+(−A+B)x−B.
Next, (Cx+D)(x−1)=Cx2+(D−C)x−D. And E(x2+1)2=Ex4+2Ex2+E.
4. Collect coefficients by power of x and equate to the right-hand side of the original equation (which is just x, so coefficients are 0,0,0,1,0 for x4,x3,x2,x1,x0 respectively):
- x4: A+E=0⇒A=−E=−41.
- x3: −A+B=0⇒B=A=−41.
- x2: (A−B)+C+2E=0. Since A=B, this gives C=−2E=−21. …
- AP EAPCET 2022Set eng-2022-07-05-FN1 markMCQQ.x3−12x2+1=x−1A+x2+x+1Bx+C⇒7A+2B+C= (A) 8 (B) 9 (C) 10 (D) 11
›Reveal solutionSolution
Clear denominators in the partial fraction decomposition, use x=1 to find A quickly, then match coefficients for B and C.
Concept and Intuition
Since x3−1=(x−1)(x2+x+1), the partial fraction form given is standard. Plugging in the root of the linear factor (x=1) isolates A immediately; matching remaining coefficients (or plugging in more values) gives B,C.
Step-by-Step Solution
- Multiply both sides by x3−1=(x−1)(x2+x+1): 2x2+1=A(x2+x+1)+(Bx+C)(x−1).
- Set x=1: 2(1)+1=A(1+1+1)+0⇒3=3A⇒A=1.
- Expand the right side: Ax2+Ax+A+Bx2−Bx+Cx−C=(A+B)x2+(A−B+C)x+(A−C).
- Match x2 coefficient: A+B=2⇒B=2−1=1.
- Match constant term: A−C=1⇒C=A−1=0. …
- AP EAPCET 2024Set eng-2024-05-20-FN1 markMCQQ.∫(x2−4)(x2+1)2x2−3dx=Atan−1x+Blog(x−2)+Clog(x+2) then 6A+7B−5C= (A) 9 (B) 10 (C) 6 (D) 8
›Reveal solutionSolution
Partial fractions of a rational function whose denominator has both real linear factors and an irreducible quadratic factor; the required integral form pins down the decomposition.
Concept and Intuition
The target antiderivative form Atan−1x+Blog(x−2)+Clog(x+2) tells us exactly what partial-fraction decomposition must have produced it: a term A/(x2+1) (integrates to Atan−1x), and terms B/(x−2), C/(x+2).
Step-by-Step Solution
- Write (x−2)(x+2)(x2+1)2x2−3=x2+1A+x−2B+x+2C.
- Multiply through: 2x2−3=A(x2−4)+B(x+2)(x2+1)+C(x−2)(x2+1).
- Set x=2: 5=A(0)+B(4)(5)+0⇒20B=5⇒B=41.
- Set x=−2: 5=0+0+C(−4)(5)⇒−20C=5⇒C=−41. …
- AP EAPCET 2026Set eng-2026-05-14-FN1 markMCQQ.∫x2−5x+4xdx= (A) 31log∣x−1∣(x−4)4+c (B) 34log(x−1)4∣x−4∣+c (C) −31log∣x−1∣(x−4)2 (D) −34log(x−1)4∣x−4∣+c
›Reveal solutionSolution
Partial fraction decomposition of a rational function with distinct linear factors, followed by direct log integration and recombination, gives 31log∣x−1∣(x−4)4+c.
Concept and Intuition
Whenever the denominator of a rational integrand factors into distinct linear terms, partial fractions break it into simpler pieces, each of which integrates to a logarithm. Combining the two resulting logarithm terms back into a single log-of-a-ratio (using log rules alogm−blogn=lognbma) is what makes the answer match a compact multiple-choice form.
Step-by-Step Solution
- Factor the denominator: x2−5x+4=(x−1)(x−4).
- Write (x−1)(x−4)x=x−1A+x−4B.
- Multiply through: x=A(x−4)+B(x−1).
- Set x=1: 1=A(1−4)=−3A⇒A=−31.
- Set x=4: 4=B(4−1)=3B⇒B=34.
- So the integral is ∫(−x−11/3+x−44/3)dx=−31log∣x−1∣+34log∣x−4∣+c. …
- AP EAPCET 2022Set eng-2022-07-08-FN1 markMCQQ.If (x−1)(x2+1)2x=41[x−11−x2+1x+1]+y, then y= (A) 21[(x2+1)21−x] (B) 3(x2+1)21+x (C) (x2−1)21−x (D) (x2+1)21+x
›Reveal solutionSolution
This tests partial fraction decomposition with a repeated irreducible quadratic factor, then matching the remaining unaccounted term to y.
Concept and Intuition
For a denominator (x−1)(x2+1)2, the full decomposition has the form x−1A+x2+1Bx+C+(x2+1)2Dx+E. The problem already gives the first two pieces combined as 41[x−11−x2+1x+1], so y must be exactly the third piece.
Step-by-Step Solution
- Write (x−1)(x2+1)2x=x−1A+x2+1Bx+C+(x2+1)2Dx+E.
- Multiply through: x=A(x2+1)2+(Bx+C)(x−1)(x2+1)+(Dx+E)(x−1).
- Set x=1: 1=4A⇒A=41.
- Expand and match coefficients of x4,x3,x2,x1,x0: this yields B=−41, C=−41, D=−21, E=21.
- So the full decomposition is x−11/4−41⋅x2+1x+1+(x2+1)2(1−x)/2. …
- AP EAPCET 2021Set eng-2021-08-24-FN1 markMCQQ.Which of the following is an improper rational traction? (A) (x2+2)(x2+x+1)x2+1 (B) (x+3)(x2−x+1)x2+1 (C) (x2+3x+1)x (D) x2−1x2+1
›Reveal solutionSolution
A rational fraction is proper only when the numerator's degree is strictly less than the denominator's; option (D) has numerator and denominator of the same degree (2 and 2), making it the only improper fraction listed.
Concept and Intuition
In partial fraction decomposition, a "proper" rational fraction has numerator degree strictly less than denominator degree, ensuring the fraction tends to zero as x→∞ and decomposes cleanly into partial fractions without needing polynomial long division first. An "improper" fraction (numerator degree ≥ denominator degree) must first be reduced via division into a polynomial plus a proper remainder fraction.
Step-by-Step Solution
- Option (A): (x2+2)(x2+x+1)x2+1 — numerator degree 2; denominator is a product of two quadratics, degree 2+2=4. Since 2<4, this is proper.
- Option (B): (x+3)(x2−x+1)x2+1 — numerator degree 2; denominator is linear times quadratic, degree 1+2=3. Since 2<3, proper.
- Option (C): x2+3x+1x — numerator degree 1; denominator degree 2. Since 1<2, proper. …
- AP EAPCET 2026Set eng-2026-05-14-AN1 markMCQQ.One of the partial fractions of (x2+2)(3x−1)2x2+x−3 is (A) 19(3x−1)22 (B) 19(x2+2)20x−13 (C) 19(x2+2)20x+13 (D) 3x−122
›Reveal solutionSolution
Standard partial-fraction decomposition with one irreducible quadratic factor and one linear factor. Solving for the constants gives A=1920,B=1913,C=−1922, so the quadratic-denominator fraction is 19(x2+2)20x+13.
Concept and Intuition
Since x2+2 has no real roots, it contributes a fraction with a linear numerator Ax+B, while the linear factor 3x−1 contributes a constant numerator C. Clearing denominators turns the problem into matching coefficients (or, more efficiently, substituting convenient values of x — especially the root of the linear factor, which instantly isolates C).
Step-by-Step Solution
- Set up: 2x2+x−3=(Ax+B)(3x−1)+C(x2+2).
- Substitute x=31 (root of 3x−1), which kills the (Ax+B)(3x−1) term:
2(91)+31−3=C(91+2)⇒92+3−27=C⋅919⇒−922=919C⇒C=−1922.
- Substitute x=0: LHS =−3; RHS =B(−1)+2C=−B+2(−1922)=−B−1944.
−3=−B−1944⇒B=1944−3=1944−57=−1913...
Recheck sign: −3=−B−1944⇒−B=−3+1944=19−57+44=−1913⇒B=1913.
4. Substitute x=1: LHS =2+1−3=0; RHS =(A+B)(2)+3C=2A+2B+3C.
0=2A+2(1913)+3(−1922)=2A+1926−66=2A−1940⇒A=1920. …
- AP EAPCET 2026Set eng-2026-05-15-AN1 markMCQQ.If (x+2)2A is one of the partial fractions of (2x+1)(x+2)2x2+3x+5, then A= (A) 2 (B) 1 (C) -2 (D) -1
›Reveal solutionSolution
Using the cover-up (Heaviside) method at the repeated root x=−2 gives A=−1 directly, no full partial-fraction expansion needed.
Concept and Intuition
For a repeated linear factor (x+2)2 in the denominator, the partial fraction decomposition has a term (x+2)2A whose coefficient can be found by the cover-up method: multiply both sides by (x+2)2, which cancels that factor from the denominator entirely, then substitute x=−2 into what remains (the other terms of the decomposition vanish or become finite/zero at this special substitution for the squared-factor coefficient specifically).
Step-by-Step Solution
- Write (2x+1)(x+2)2x2+3x+5=2x+1P+x+2Q+(x+2)2A.
- Multiply both sides by (x+2)2: 2x+1x2+3x+5=P⋅2x+1(x+2)2+Q(x+2)+A.
- Substitute x=−2 (this kills the P and Q terms since they still carry a factor of (x+2)): A=2x+1x2+3x+5x=−2. …
- AP EAPCET 2025Set eng-2025-05-22-FN1 markMCQQ.If (x−1)2(x2+1)x+1=x−1A+(x−1)2B+x2+1Cx+D, then 3A2+4D2+5C2+B2= (A) 23 (B) 21 (C) 1 (D) 2
›Reveal solutionSolution
Solving the partial-fraction decomposition gives A=−21,B=1,C=21,D=−21; substituting into 3A2+4D2+5C2+B2 gives 2.
Concept and Intuition
A rational function with a repeated linear factor (x−1)2 and an irreducible quadratic factor (x2+1) decomposes as x−1A+(x−1)2B+x2+1Cx+D. Clearing denominators and matching coefficients (or plugging convenient values of x) pins down all four constants.
Step-by-Step Solution
- Multiply both sides by (x−1)2(x2+1):
x+1=A(x−1)(x2+1)+B(x2+1)+(Cx+D)(x−1)2.
- Plug x=1: LHS =2. RHS =0+B(1+1)+0=2B. So B=1.
- Expand each term:
- A(x−1)(x2+1)=A(x3−x2+x−1).
- B(x2+1)=x2+1 (using B=1).
- (Cx+D)(x−1)2=(Cx+D)(x2−2x+1)=Cx3+(−2C+D)x2+(C−2D)x+D.
- Collect coefficients and match with x+1=0⋅x3+0⋅x2+1⋅x+1:
- x3: A+C=0.
- x2: −A+1−2C+D=0.
- x1: A+C−2D=1.
- x0: −A+1+D=1.
- From x3: C=−A. Substitute into x1 equation: A−A−2D=1⇒D=−21.
- From x0: −A+D=0⇒A=D=−21, hence C=−A=21.
- (Verify x2 equation: −(−21)+1−2(21)+(−21)=21+1−1−21=0 ✓.) …
- AP EAPCET 2021Set eng-2021-08-25-AN1 markMCQQ.The partial fraction of x2+3x−4x2 is ________ (A) 1+5(x+4)−16+5(x−1)1 (B) 1+x+4−1+x−11 (C) 1+5(x+4)−13+5(x−1)1 (D) x+42+x−11
›Reveal solutionSolution
Since the numerator's degree equals the denominator's degree, perform polynomial division first, then resolve the remaining proper fraction into partial fractions. Answer: (A).
Concept and Intuition
Partial fraction decomposition applies to a proper rational function (numerator degree less than denominator degree). Here both are degree 2, so we must first extract the constant (integer) part via division, leaving a proper fraction to decompose.
Step-by-Step Solution
- Factor the denominator: x2+3x−4=(x+4)(x−1).
- Divide: x2=(x2+3x−4)−(3x−4), so x2+3x−4x2=1−(x+4)(x−1)3x−4.
- Decompose (x+4)(x−1)3x−4=x+4A+x−1B, so 3x−4=A(x−1)+B(x+4).
- Set x=1: −1=5B⇒B=−51.
- Set x=−4: −16=−5A⇒A=516.
- So (x+4)(x−1)3x−4=5(x+4)16−5(x−1)1. …
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