Q.Integrate the following function: (1−x)(1+x2)2
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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. …
Idea: a linear factor plus an irreducible quadratic, so use 1−xA+1+x2Bx+C.
(1−x)(1+x2)2=1−xA+1+x2Bx+C.
Clear denominators: 2=A(1+x2)+(Bx+C)(1−x)=(A−B)x2+(B−C)x+(A+C).
Match coefficients: A−B=0,B−C=0,A+C=2⇒A=B=C=1.
So the integral is …
Decompose into a linear piece plus a piece over 1+x2; integrating gives −log∣1−x∣+21log(1+x2)+tan−1x+C.
Setting up the decomposition
The denominator is a linear factor (1−x) times the irreducible quadratic (1+x2) (it has no real roots). An irreducible quadratic gets a linear numerator, so
(1−x)(1+x2)2=1−xA+1+x2Bx+C.
Solving for the constants
Multiply through by (1−x)(1+x2):
2=A(1+x2)+(Bx+C)(1−x).
Expand the right side: A+Ax2+Bx−Bx2+C−Cx=(A−B)x2+(B−C)x+(A+C).
Since the left side is 2=0⋅x2+0⋅x+2, match coefficients:
A−B=0,B−C=0,A+C=2.
The first two give A=B=C, and then A+C=2 gives 2A=2, so A=B=C=1. (Check: putting x=1 in the cleared equation gives 2=2A, confirming A=1.)
The decomposed form …
Method: Partial Fractions with an Irreducible Quadratic Factor
Use this when the denominator has a quadratic factor with no real roots (like 1+x2) alongside linear factors.
Steps
Step 1: Identify the irreducible quadratic.
A quadratic with negative discriminant (e.g. x2+1) cannot be split into real linear factors, so it stays intact.
Step 2: Give the irreducible quadratic a LINEAR numerator.
A degree-2 factor needs a degree-1 numerator; a linear factor keeps a constant:
(a−x)(1+x2)P(x)=a−xA+1+x2Bx+C
Step 3: Clear denominators and match coefficients of each power of x. …
Common Mistakes
Mistake 1: Putting a constant numerator over 1+x2.
Why it's wrong: an irreducible quadratic factor requires a linear numerator Bx+C; using just a constant loses a degree of freedom and the system won't solve. Correct approach: write 1+x2Bx+C.
Mistake 2: Integrating 1+x2x without the 21. …
Showing the 12 most recent of 63 on this concept.
- AP EAPCET 2021Set eng-2021-08-24-AN1 markMCQQ.∫(x−2)(x−3)x−1dx= (A) 2log∣x−3∣+log∣x−2∣+c (B) log∣x−3∣−log∣x−2∣+c (C) log∣x−3∣2−log∣x+2∣+c (D) logx−2(x−3)2+c
›Reveal solutionSolution
A rational function with distinct linear factors in the denominator — resolve into partial fractions, integrate each term as a log, then combine using log rules.
Concept and Intuition
Any proper rational function with distinct linear denominator factors can be split into simple fractions x−aA+x−bB, each of which integrates to Alog∣x−a∣. Combining the two logs at the end into a single log of a ratio/power lets you match against answer choices written as one combined logarithm.
Step-by-Step Solution
- Write (x−2)(x−3)x−1=x−2A+x−3B, so x−1=A(x−3)+B(x−2).
- Put x=2: 2−1=A(2−3)⇒1=−A⇒A=−1.
- Put x=3: 3−1=B(3−2)⇒2=B.
- So ∫(x−2)(x−3)x−1dx=−log∣x−2∣+2log∣x−3∣+c. …
- 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-2026-05-15-AN1 markMCQQ.∫sinx+sin2xdx= (A) 41log∣1−cosx∣+31log∣1+cosx∣−32log∣1+cos2x∣+c (B) 31log∣1−cosx∣+41log∣1+cosx∣+31log∣1+cos2x∣+c (C) 61log∣1−cosx∣+21log∣1+cosx∣−32log∣1+2cosx∣+c (D) 61log∣1−cosx∣+41log∣1+cosx∣+32log∣1+2cosx∣+c
›Reveal solutionSolution
Factoring sinx+sin2x=sinx(1+2cosx) and substituting t=cosx reduces this to a rational-function partial-fractions integral, giving 61log∣1−cosx∣+21log∣1+cosx∣−32log∣1+2cosx∣+c.
Concept and Intuition
Whenever an integral has sinx (an odd power effectively) times other cosine factors in the denominator, multiplying numerator and denominator by sinx turns sin2x into 1−cos2x, which lets us substitute t=cosx and reduce the whole problem to partial fractions of a rational function in t — a completely mechanical final step.
Step-by-Step Solution
- Factor the denominator: sinx+sin2x=sinx+2sinxcosx=sinx(1+2cosx).
- So the integral is ∫sinx(1+2cosx)dx.
- Multiply top and bottom by sinx: ∫sin2x(1+2cosx)sinxdx=∫(1−cos2x)(1+2cosx)sinxdx=∫(1−cosx)(1+cosx)(1+2cosx)sinxdx.
- Substitute t=cosx, dt=−sinxdx: integral =−∫(1−t)(1+t)(1+2t)dt.
- Partial fractions: (1−t)(1+t)(1+2t)1=1−tA+1+tB+1+2tC. Evaluating at t=1: A=61. At t=−1: B=21. At t=−21: C=−32. …
- AP EAPCET 2026Set eng-2026-05-15-FN1 markMCQQ.If ∫x3+x2x3−1dx=f(x)+log(g(x))+c, f(1)=2 and g(−3)=43, then f(−2)+g(−2)= (A) −29 (B) −21 (C) 49 (D) 41
›Reveal solutionSolution
A rational-function integral splits by partial fractions into a polynomial/rational part f(x) plus a logarithmic part log(g(x)); the two given data points pin down f and g exactly, letting us evaluate f(−2)+g(−2). Answer: −21.
Concept and Intuition
When an improper rational integrand is written x3+x2x3−1, polynomial division peels off the constant part, and partial fractions turn the remaining proper fraction into simple terms of the form xA,x2B,x+1C whose antiderivatives are Alog∣x∣, −B/x, Clog∣x+1∣. Collecting all log terms into a single log(g(x)) and all algebraic terms into f(x) matches the form the question gives; the two numeric conditions are just there to confirm the constants (and resolve the sign inside the absolute value at negative x).
Step-by-Step Solution
- Divide: x3+x2x3−1=1−x3+x2x2+1=1−x2(x+1)x2+1.
- Partial fractions: x2(x+1)x2+1=xA+x2B+x+1C. Clearing denominators: x2+1=Ax(x+1)+B(x+1)+Cx2. Setting x=0: B=1. Setting x=−1: 2=C. Matching x2 coefficients: 1=A+C⇒A=−1.
- So x2(x+1)x2+1=−x1+x21+x+12, and the integrand is 1+x1−x21−x+12.
- Integrate term by term: ∫(1+x1−x21−x+12)dx=x+log∣x∣+x1−2log∣x+1∣+c=(x+x1)+log(x+1)2x+c. …
- 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 2025Set eng-2025-05-26-FN1 markMCQQ.If (x−1)(x−2)x4=f(x)+x−1A+x−2B, then f(−2)+A+B= (A) 32 (B) 28 (C) 22 (D) 20
›Reveal solutionSolution
This tests polynomial long division combined with partial fractions — split (x−1)(x−2)x4 into a polynomial part f(x) plus proper fractions. Answer: f(−2)+A+B=20.
Concept and Intuition
When the numerator's degree (4) is greater than or equal to the denominator's degree (2), a rational function isn't purely a sum of partial fractions — you first must divide out a polynomial quotient f(x), leaving a proper-fraction remainder that partial-fractions cleanly. Here f(x) is exactly that quotient (degree 4−2=2).
Step-by-Step Solution
- Divide x4 by x2−3x+2 (long division): x4=(x2−3x+2)(x2+3x+7)+(15x−14) Check: (x2−3x+2)(x2+3x+7)=x4−15x+14, so adding 15x−14 recovers x4. ✓
- So f(x)=x2+3x+7, and the remainder gives (x−1)(x−2)15x−14=x−1A+x−2B.
- Clear denominators: 15x−14=A(x−2)+B(x−1).
- Put x=1: 15−14=A(−1)⇒1=−A⇒A=−1. …
- AP EAPCET 2026Set eng-2026-05-12-AN1 markMCQQ.If (x2−1)24x=x−1A1+(x−1)2A2+x+1A3+(x+1)2A4, then A1+A2+A3+A4= (A) −2 (B) 1 (C) 0 (D) 23
›Reveal solutionSolution
Clearing denominators and substituting convenient values of x (the repeated roots plus two extra points) pins down all four constants; they add up to 0.
Concept and Intuition
For a partial fraction decomposition with repeated linear factors, substituting the roots directly isolates the "squared-term" coefficients instantly, while substituting a couple of extra convenient values (like x=0 and x=2) gives enough equations to solve for the remaining linear-term coefficients.
Step-by-Step Solution
- Multiply both sides by (x−1)2(x+1)2:
4x=A1(x−1)(x+1)2+A2(x+1)2+A3(x+1)(x−1)2+A4(x−1)2.
- Set x=1: 4=A2(2)2=4A2⇒A2=1.
- Set x=−1: −4=A4(−2)2=4A4⇒A4=−1.
- Set x=0: 0=A1(−1)(1)+A2(1)+A3(1)(1)+A4(1)=−A1+A2+A3+A4. Using A2=1,A4=−1: 0=−A1+A3⇒A1=A3. …
- 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 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 2021Set eng-2021-08-19-FN1 markMCQQ.If (x−1)(x−2)x4=f(x)+x−1A+x−2B, then (A) f(x)=x2−3x+7 (B) f(x)=x2+3x+7 (C) A+B=17 (D) A−B=−18
›Reveal solutionSolution
Dividing x4 by (x−1)(x−2) gives quotient f(x)=x2+3x+7 with remainder 15x−14, and partial-fractioning the remainder gives A=−1,B=16 — so only the f(x) option is correct.
Concept and Intuition
When a rational function's numerator degree exceeds the denominator's, you must first do polynomial long division to extract the polynomial part f(x) before decomposing the proper-fraction remainder into partial fractions. Skipping the division step and partial-fractioning directly would be invalid since (x−1)(x−2)x4 isn't a proper fraction.
Step-by-Step Solution
- Divide x4 by x2−3x+2 (the denominator's product):
- x4÷x2=x2; x2(x2−3x+2)=x4−3x3+2x2; subtract: 3x3−2x2.
- 3x3÷x2=3x; 3x(x2−3x+2)=3x3−9x2+6x; subtract: 7x2−6x.
- 7x2÷x2=7; 7(x2−3x+2)=7x2−21x+14; subtract: 15x−14.
- So x4=(x2−3x+2)(x2+3x+7)+(15x−14), giving f(x)=x2+3x+7 and remainder 15x−14.
- Decompose (x−1)(x−2)15x−14=x−1A+x−2B: so 15x−14=A(x−2)+B(x−1).
- At x=1: 15−14=1=A(−1)⇒A=−1. …
- Divide x4 by x2−3x+2 (the denominator's product):
- 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-FN1 markMCQQ.If (1+x2)(3−2x)x=1+x2Bx+C+3−2xA, then 'C' is (A) 32 (B) 131 (C) −131 (D) −132
›Reveal solutionSolution
Clearing denominators and matching coefficients of the partial-fraction identity gives C=−2/13.
Concept and Intuition
Partial fraction decomposition works by clearing all denominators to get a polynomial identity valid for all x, then equating coefficients of like powers of x on both sides.
Step-by-Step Solution
- Multiply both sides by (1+x2)(3−2x): x=(Bx+C)(3−2x)+A(1+x2).
- Expand: (Bx+C)(3−2x)=−2Bx2+(3B−2C)x+3C, and A(1+x2)=Ax2+A.
- Combine: (A−2B)x2+(3B−2C)x+(3C+A)=x.
- Match coefficients:
- x2: A−2B=0⇒A=2B.
- x1: 3B−2C=1.
- x0: 3C+A=0⇒A=−3C. …
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