Hard A-Level Integration with partial fractions Questions

Challenging, exam-style A-Level Integration with partial fractions questions with worked solutions. Stretch yourself on the hardest partial fractions, integration problems.

partial fractionsintegration
A-Level34 questionsStep-by-step solutions
Question 1
8 markschallenging
Which of the following is equal to 3x2+1(x4)(x1)(x+2)dx\int \frac{3 x^{2} + 1}{\left(x - 4\right) \left(x - 1\right) \left(x + 2\right)}\,dx?
Show worked solution

Worked solution

  1. Write down the integral

    3x2+1(x4)(x1)(x+2)dx\int \frac{3 x^{2} + 1}{\left(x - 4\right) \left(x - 1\right) \left(x + 2\right)}\,dx

    We integrate this rational function by first splitting it into partial fractions.

  2. Factorise the denominator

    x33x26x+8=(x4)(x1)(x+2)x^{3} - 3 x^{2} - 6 x + 8=\left(x - 4\right) \left(x - 1\right) \left(x + 2\right)

    The linear factors tell us the form of the partial fractions.

  3. Set up the partial fraction form

    3x2+1(x4)(x1)(x+2)Ax+2+Bx1+Cx4\frac{3 x^{2} + 1}{\left(x - 4\right) \left(x - 1\right) \left(x + 2\right)}\equiv \frac{A}{x + 2}+\frac{B}{x - 1}+\frac{C}{x - 4}

    Write one constant over each distinct linear factor.

  4. Multiply through by the denominator

    3x2+1A((x4)(x1))+B((x4)(x+2))+C((x1)(x+2))3 x^{2} + 1\equiv A\left(\left(x - 4\right) \left(x - 1\right)\right)+B\left(\left(x - 4\right) \left(x + 2\right)\right)+C\left(\left(x - 1\right) \left(x + 2\right)\right)

    Clearing the fractions gives an identity valid for all x.

  5. Substitute x=-2 to find A

    A=1318A=\frac{13}{18}

    This choice of x makes the other unknowns vanish (cover-up method).

  6. Substitute x=1 to find B

    B=49B=- \frac{4}{9}

    This choice of x makes the other unknowns vanish (cover-up method).

  7. Substitute x=4 to find C

    C=4918C=\frac{49}{18}

    This choice of x makes the other unknowns vanish (cover-up method).

  8. Collect the constants

    A=1318, B=49, C=4918A=\frac{13}{18},\ B=- \frac{4}{9},\ C=\frac{49}{18}

    These constants complete the decomposition.

  9. Write the partial fraction decomposition

    3x2+1(x4)(x1)(x+2)1318(x+2)49(x1)+4918(x4)\frac{3 x^{2} + 1}{\left(x - 4\right) \left(x - 1\right) \left(x + 2\right)}\equiv \frac{13}{18 \left(x + 2\right)} - \frac{4}{9 \left(x - 1\right)} + \frac{49}{18 \left(x - 4\right)}

    Each simple fraction is now easy to integrate.

  10. Split into standard integrals

    3x2+1(x4)(x1)(x+2)dx=1318(x+2)dx+49(x1)dx+4918(x4)dx\int \frac{3 x^{2} + 1}{\left(x - 4\right) \left(x - 1\right) \left(x + 2\right)}\,dx=\int \frac{13}{18 \left(x + 2\right)}\,dx+\int - \frac{4}{9 \left(x - 1\right)}\,dx+\int \frac{49}{18 \left(x - 4\right)}\,dx

    Each term of the form k/(x-a) integrates to a logarithm.

  11. Integrate the first term

    1318(x+2)dx=13ln(18x+36)18\int \frac{13}{18 \left(x + 2\right)}\,dx=\frac{13 \ln{\left(18 x + 36 \right)}}{18}

    Use \int \frac{k}{x-a}\,dx=k\ln|x-a|.

  12. Integrate the second term

    49(x1)dx=4ln(9x9)9\int - \frac{4}{9 \left(x - 1\right)}\,dx=- \frac{4 \ln{\left(9 x - 9 \right)}}{9}

    Use \int \frac{k}{x-a}\,dx=k\ln|x-a|.

  13. Integrate the third term

    4918(x4)dx=49ln(18x72)18\int \frac{49}{18 \left(x - 4\right)}\,dx=\frac{49 \ln{\left(18 x - 72 \right)}}{18}

    Use \int \frac{k}{x-a}\,dx=k\ln|x-a|.

  14. Combine the integrated terms

    49ln(x4)184ln(x1)9+13ln(x+2)18\frac{49 \ln{\left(x - 4 \right)}}{18} - \frac{4 \ln{\left(x - 1 \right)}}{9} + \frac{13 \ln{\left(x + 2 \right)}}{18}

    Add the logarithmic terms to form the antiderivative.

  15. Select the correct option

    49ln(x4)184ln(x1)9+13ln(x+2)18+c\frac{49 \ln{\left(x - 4 \right)}}{18} - \frac{4 \ln{\left(x - 1 \right)}}{9} + \frac{13 \ln{\left(x + 2 \right)}}{18} + c

    The option matching the integrated decomposition is the correct answer.

Answer
49ln(x4)184ln(x1)9+13ln(x+2)18+c\frac{49 \ln{\left(x - 4 \right)}}{18} - \frac{4 \ln{\left(x - 1 \right)}}{9} + \frac{13 \ln{\left(x + 2 \right)}}{18} + c
Question 2
8 markschallenging
Which of the following is equal to x2+5(x3)(x1)(x+2)dx\int \frac{x^{2} + 5}{\left(x - 3\right) \left(x - 1\right) \left(x + 2\right)}\,dx?
Show worked solution

Worked solution

  1. Write down the integral

    x2+5(x3)(x1)(x+2)dx\int \frac{x^{2} + 5}{\left(x - 3\right) \left(x - 1\right) \left(x + 2\right)}\,dx

    We integrate this rational function by first splitting it into partial fractions.

  2. Factorise the denominator

    x32x25x+6=(x3)(x1)(x+2)x^{3} - 2 x^{2} - 5 x + 6=\left(x - 3\right) \left(x - 1\right) \left(x + 2\right)

    The linear factors tell us the form of the partial fractions.

  3. Set up the partial fraction form

    x2+5(x3)(x1)(x+2)Ax+2+Bx1+Cx3\frac{x^{2} + 5}{\left(x - 3\right) \left(x - 1\right) \left(x + 2\right)}\equiv \frac{A}{x + 2}+\frac{B}{x - 1}+\frac{C}{x - 3}

    Write one constant over each distinct linear factor.

  4. Multiply through by the denominator

    x2+5A((x3)(x1))+B((x3)(x+2))+C((x1)(x+2))x^{2} + 5\equiv A\left(\left(x - 3\right) \left(x - 1\right)\right)+B\left(\left(x - 3\right) \left(x + 2\right)\right)+C\left(\left(x - 1\right) \left(x + 2\right)\right)

    Clearing the fractions gives an identity valid for all x.

  5. Substitute x=-2 to find A

    A=35A=\frac{3}{5}

    This choice of x makes the other unknowns vanish (cover-up method).

  6. Substitute x=1 to find B

    B=1B=-1

    This choice of x makes the other unknowns vanish (cover-up method).

  7. Substitute x=3 to find C

    C=75C=\frac{7}{5}

    This choice of x makes the other unknowns vanish (cover-up method).

  8. Collect the constants

    A=35, B=1, C=75A=\frac{3}{5},\ B=-1,\ C=\frac{7}{5}

    These constants complete the decomposition.

  9. Write the partial fraction decomposition

    x2+5(x3)(x1)(x+2)35(x+2)1x1+75(x3)\frac{x^{2} + 5}{\left(x - 3\right) \left(x - 1\right) \left(x + 2\right)}\equiv \frac{3}{5 \left(x + 2\right)} - \frac{1}{x - 1} + \frac{7}{5 \left(x - 3\right)}

    Each simple fraction is now easy to integrate.

  10. Split into standard integrals

    x2+5(x3)(x1)(x+2)dx=35(x+2)dx+1x1dx+75(x3)dx\int \frac{x^{2} + 5}{\left(x - 3\right) \left(x - 1\right) \left(x + 2\right)}\,dx=\int \frac{3}{5 \left(x + 2\right)}\,dx+\int - \frac{1}{x - 1}\,dx+\int \frac{7}{5 \left(x - 3\right)}\,dx

    Each term of the form k/(x-a) integrates to a logarithm.

  11. Integrate the first term

    35(x+2)dx=3ln(5x+10)5\int \frac{3}{5 \left(x + 2\right)}\,dx=\frac{3 \ln{\left(5 x + 10 \right)}}{5}

    Use \int \frac{k}{x-a}\,dx=k\ln|x-a|.

  12. Integrate the second term

    1x1dx=ln(x1)\int - \frac{1}{x - 1}\,dx=- \ln{\left(x - 1 \right)}

    Use \int \frac{k}{x-a}\,dx=k\ln|x-a|.

  13. Integrate the third term

    75(x3)dx=7ln(5x15)5\int \frac{7}{5 \left(x - 3\right)}\,dx=\frac{7 \ln{\left(5 x - 15 \right)}}{5}

    Use \int \frac{k}{x-a}\,dx=k\ln|x-a|.

  14. Combine the integrated terms

    7ln(x3)5ln(x1)+3ln(x+2)5\frac{7 \ln{\left(x - 3 \right)}}{5} - \ln{\left(x - 1 \right)} + \frac{3 \ln{\left(x + 2 \right)}}{5}

    Add the logarithmic terms to form the antiderivative.

  15. Select the correct option

    7ln(x3)5ln(x1)+3ln(x+2)5+c\frac{7 \ln{\left(x - 3 \right)}}{5} - \ln{\left(x - 1 \right)} + \frac{3 \ln{\left(x + 2 \right)}}{5} + c

    The option matching the integrated decomposition is the correct answer.

Answer
7ln(x3)5ln(x1)+3ln(x+2)5+c\frac{7 \ln{\left(x - 3 \right)}}{5} - \ln{\left(x - 1 \right)} + \frac{3 \ln{\left(x + 2 \right)}}{5} + c
Question 3
8 markschallenging
Which of the following is equal to x2+x+1(x2)(x1)(x+1)dx\int \frac{x^{2} + x + 1}{\left(x - 2\right) \left(x - 1\right) \left(x + 1\right)}\,dx?
Show worked solution

Worked solution

  1. Write down the integral

    x2+x+1(x2)(x1)(x+1)dx\int \frac{x^{2} + x + 1}{\left(x - 2\right) \left(x - 1\right) \left(x + 1\right)}\,dx

    We integrate this rational function by first splitting it into partial fractions.

  2. Factorise the denominator

    x32x2x+2=(x2)(x1)(x+1)x^{3} - 2 x^{2} - x + 2=\left(x - 2\right) \left(x - 1\right) \left(x + 1\right)

    The linear factors tell us the form of the partial fractions.

  3. Set up the partial fraction form

    x2+x+1(x2)(x1)(x+1)Ax+1+Bx1+Cx2\frac{x^{2} + x + 1}{\left(x - 2\right) \left(x - 1\right) \left(x + 1\right)}\equiv \frac{A}{x + 1}+\frac{B}{x - 1}+\frac{C}{x - 2}

    Write one constant over each distinct linear factor.

  4. Multiply through by the denominator

    x2+x+1A((x2)(x1))+B((x2)(x+1))+C((x1)(x+1))x^{2} + x + 1\equiv A\left(\left(x - 2\right) \left(x - 1\right)\right)+B\left(\left(x - 2\right) \left(x + 1\right)\right)+C\left(\left(x - 1\right) \left(x + 1\right)\right)

    Clearing the fractions gives an identity valid for all x.

  5. Substitute x=-1 to find A

    A=16A=\frac{1}{6}

    This choice of x makes the other unknowns vanish (cover-up method).

  6. Substitute x=1 to find B

    B=32B=- \frac{3}{2}

    This choice of x makes the other unknowns vanish (cover-up method).

  7. Substitute x=2 to find C

    C=73C=\frac{7}{3}

    This choice of x makes the other unknowns vanish (cover-up method).

  8. Collect the constants

    A=16, B=32, C=73A=\frac{1}{6},\ B=- \frac{3}{2},\ C=\frac{7}{3}

    These constants complete the decomposition.

  9. Write the partial fraction decomposition

    x2+x+1(x2)(x1)(x+1)16(x+1)32(x1)+73(x2)\frac{x^{2} + x + 1}{\left(x - 2\right) \left(x - 1\right) \left(x + 1\right)}\equiv \frac{1}{6 \left(x + 1\right)} - \frac{3}{2 \left(x - 1\right)} + \frac{7}{3 \left(x - 2\right)}

    Each simple fraction is now easy to integrate.

  10. Split into standard integrals

    x2+x+1(x2)(x1)(x+1)dx=16(x+1)dx+32(x1)dx+73(x2)dx\int \frac{x^{2} + x + 1}{\left(x - 2\right) \left(x - 1\right) \left(x + 1\right)}\,dx=\int \frac{1}{6 \left(x + 1\right)}\,dx+\int - \frac{3}{2 \left(x - 1\right)}\,dx+\int \frac{7}{3 \left(x - 2\right)}\,dx

    Each term of the form k/(x-a) integrates to a logarithm.

  11. Integrate the first term

    16(x+1)dx=ln(6x+6)6\int \frac{1}{6 \left(x + 1\right)}\,dx=\frac{\ln{\left(6 x + 6 \right)}}{6}

    Use \int \frac{k}{x-a}\,dx=k\ln|x-a|.

  12. Integrate the second term

    32(x1)dx=3ln(2x2)2\int - \frac{3}{2 \left(x - 1\right)}\,dx=- \frac{3 \ln{\left(2 x - 2 \right)}}{2}

    Use \int \frac{k}{x-a}\,dx=k\ln|x-a|.

  13. Integrate the third term

    73(x2)dx=7ln(3x6)3\int \frac{7}{3 \left(x - 2\right)}\,dx=\frac{7 \ln{\left(3 x - 6 \right)}}{3}

    Use \int \frac{k}{x-a}\,dx=k\ln|x-a|.

  14. Combine the integrated terms

    7ln(x2)33ln(x1)2+ln(x+1)6\frac{7 \ln{\left(x - 2 \right)}}{3} - \frac{3 \ln{\left(x - 1 \right)}}{2} + \frac{\ln{\left(x + 1 \right)}}{6}

    Add the logarithmic terms to form the antiderivative.

  15. Select the correct option

    7ln(x2)33ln(x1)2+ln(x+1)6+c\frac{7 \ln{\left(x - 2 \right)}}{3} - \frac{3 \ln{\left(x - 1 \right)}}{2} + \frac{\ln{\left(x + 1 \right)}}{6} + c

    The option matching the integrated decomposition is the correct answer.

Answer
7ln(x2)33ln(x1)2+ln(x+1)6+c\frac{7 \ln{\left(x - 2 \right)}}{3} - \frac{3 \ln{\left(x - 1 \right)}}{2} + \frac{\ln{\left(x + 1 \right)}}{6} + c
Question 4
8 markschallenging
The expression 2x2+1(x3)(x2)(x+1)\frac{2 x^{2} + 1}{\left(x - 3\right) \left(x - 2\right) \left(x + 1\right)} is written in partial fractions. Which option is correct?
Show worked solution

Worked solution

  1. Write down the integral

    2x2+1(x3)(x2)(x+1)dx\int \frac{2 x^{2} + 1}{\left(x - 3\right) \left(x - 2\right) \left(x + 1\right)}\,dx

    We integrate this rational function by first splitting it into partial fractions.

  2. Factorise the denominator

    x34x2+x+6=(x3)(x2)(x+1)x^{3} - 4 x^{2} + x + 6=\left(x - 3\right) \left(x - 2\right) \left(x + 1\right)

    The linear factors tell us the form of the partial fractions.

  3. Set up the partial fraction form

    2x2+1(x3)(x2)(x+1)Ax+1+Bx2+Cx3\frac{2 x^{2} + 1}{\left(x - 3\right) \left(x - 2\right) \left(x + 1\right)}\equiv \frac{A}{x + 1}+\frac{B}{x - 2}+\frac{C}{x - 3}

    Write one constant over each distinct linear factor.

  4. Multiply through by the denominator

    2x2+1A((x3)(x2))+B((x3)(x+1))+C((x2)(x+1))2 x^{2} + 1\equiv A\left(\left(x - 3\right) \left(x - 2\right)\right)+B\left(\left(x - 3\right) \left(x + 1\right)\right)+C\left(\left(x - 2\right) \left(x + 1\right)\right)

    Clearing the fractions gives an identity valid for all x.

  5. Substitute x=-1 to find A

    A=14A=\frac{1}{4}

    This choice of x makes the other unknowns vanish (cover-up method).

  6. Substitute x=2 to find B

    B=3B=-3

    This choice of x makes the other unknowns vanish (cover-up method).

  7. Substitute x=3 to find C

    C=194C=\frac{19}{4}

    This choice of x makes the other unknowns vanish (cover-up method).

  8. Collect the constants

    A=14, B=3, C=194A=\frac{1}{4},\ B=-3,\ C=\frac{19}{4}

    These constants complete the decomposition.

  9. Write the partial fraction decomposition

    2x2+1(x3)(x2)(x+1)14(x+1)3x2+194(x3)\frac{2 x^{2} + 1}{\left(x - 3\right) \left(x - 2\right) \left(x + 1\right)}\equiv \frac{1}{4 \left(x + 1\right)} - \frac{3}{x - 2} + \frac{19}{4 \left(x - 3\right)}

    Each simple fraction is now easy to integrate.

  10. Split into standard integrals

    2x2+1(x3)(x2)(x+1)dx=14(x+1)dx+3x2dx+194(x3)dx\int \frac{2 x^{2} + 1}{\left(x - 3\right) \left(x - 2\right) \left(x + 1\right)}\,dx=\int \frac{1}{4 \left(x + 1\right)}\,dx+\int - \frac{3}{x - 2}\,dx+\int \frac{19}{4 \left(x - 3\right)}\,dx

    Each term of the form k/(x-a) integrates to a logarithm.

  11. Integrate the first term

    14(x+1)dx=ln(4x+4)4\int \frac{1}{4 \left(x + 1\right)}\,dx=\frac{\ln{\left(4 x + 4 \right)}}{4}

    Use \int \frac{k}{x-a}\,dx=k\ln|x-a|.

  12. Integrate the second term

    3x2dx=3ln(x2)\int - \frac{3}{x - 2}\,dx=- 3 \ln{\left(x - 2 \right)}

    Use \int \frac{k}{x-a}\,dx=k\ln|x-a|.

  13. Integrate the third term

    194(x3)dx=19ln(4x12)4\int \frac{19}{4 \left(x - 3\right)}\,dx=\frac{19 \ln{\left(4 x - 12 \right)}}{4}

    Use \int \frac{k}{x-a}\,dx=k\ln|x-a|.

  14. Combine the integrated terms

    19ln(x3)43ln(x2)+ln(x+1)4\frac{19 \ln{\left(x - 3 \right)}}{4} - 3 \ln{\left(x - 2 \right)} + \frac{\ln{\left(x + 1 \right)}}{4}

    Add the logarithmic terms to form the antiderivative.

  15. Select the correct option

    14(x+1)3x2+194(x3)\frac{1}{4 \left(x + 1\right)} - \frac{3}{x - 2} + \frac{19}{4 \left(x - 3\right)}

    The option matching the constants found is the correct answer.

Answer
14(x+1)3x2+194(x3)\frac{1}{4 \left(x + 1\right)} - \frac{3}{x - 2} + \frac{19}{4 \left(x - 3\right)}
Question 5
8 markschallenging
The expression x2+2(x3)(x1)(x+1)\frac{x^{2} + 2}{\left(x - 3\right) \left(x - 1\right) \left(x + 1\right)} is written in partial fractions. Which option is correct?
Show worked solution

Worked solution

  1. Write down the integral

    x2+2(x3)(x1)(x+1)dx\int \frac{x^{2} + 2}{\left(x - 3\right) \left(x - 1\right) \left(x + 1\right)}\,dx

    We integrate this rational function by first splitting it into partial fractions.

  2. Factorise the denominator

    x33x2x+3=(x3)(x1)(x+1)x^{3} - 3 x^{2} - x + 3=\left(x - 3\right) \left(x - 1\right) \left(x + 1\right)

    The linear factors tell us the form of the partial fractions.

  3. Set up the partial fraction form

    x2+2(x3)(x1)(x+1)Ax+1+Bx1+Cx3\frac{x^{2} + 2}{\left(x - 3\right) \left(x - 1\right) \left(x + 1\right)}\equiv \frac{A}{x + 1}+\frac{B}{x - 1}+\frac{C}{x - 3}

    Write one constant over each distinct linear factor.

  4. Multiply through by the denominator

    x2+2A((x3)(x1))+B((x3)(x+1))+C((x1)(x+1))x^{2} + 2\equiv A\left(\left(x - 3\right) \left(x - 1\right)\right)+B\left(\left(x - 3\right) \left(x + 1\right)\right)+C\left(\left(x - 1\right) \left(x + 1\right)\right)

    Clearing the fractions gives an identity valid for all x.

  5. Substitute x=-1 to find A

    A=38A=\frac{3}{8}

    This choice of x makes the other unknowns vanish (cover-up method).

  6. Substitute x=1 to find B

    B=34B=- \frac{3}{4}

    This choice of x makes the other unknowns vanish (cover-up method).

  7. Substitute x=3 to find C

    C=118C=\frac{11}{8}

    This choice of x makes the other unknowns vanish (cover-up method).

  8. Collect the constants

    A=38, B=34, C=118A=\frac{3}{8},\ B=- \frac{3}{4},\ C=\frac{11}{8}

    These constants complete the decomposition.

  9. Write the partial fraction decomposition

    x2+2(x3)(x1)(x+1)38(x+1)34(x1)+118(x3)\frac{x^{2} + 2}{\left(x - 3\right) \left(x - 1\right) \left(x + 1\right)}\equiv \frac{3}{8 \left(x + 1\right)} - \frac{3}{4 \left(x - 1\right)} + \frac{11}{8 \left(x - 3\right)}

    Each simple fraction is now easy to integrate.

  10. Split into standard integrals

    x2+2(x3)(x1)(x+1)dx=38(x+1)dx+34(x1)dx+118(x3)dx\int \frac{x^{2} + 2}{\left(x - 3\right) \left(x - 1\right) \left(x + 1\right)}\,dx=\int \frac{3}{8 \left(x + 1\right)}\,dx+\int - \frac{3}{4 \left(x - 1\right)}\,dx+\int \frac{11}{8 \left(x - 3\right)}\,dx

    Each term of the form k/(x-a) integrates to a logarithm.

  11. Integrate the first term

    38(x+1)dx=3ln(8x+8)8\int \frac{3}{8 \left(x + 1\right)}\,dx=\frac{3 \ln{\left(8 x + 8 \right)}}{8}

    Use \int \frac{k}{x-a}\,dx=k\ln|x-a|.

  12. Integrate the second term

    34(x1)dx=3ln(4x4)4\int - \frac{3}{4 \left(x - 1\right)}\,dx=- \frac{3 \ln{\left(4 x - 4 \right)}}{4}

    Use \int \frac{k}{x-a}\,dx=k\ln|x-a|.

  13. Integrate the third term

    118(x3)dx=11ln(8x24)8\int \frac{11}{8 \left(x - 3\right)}\,dx=\frac{11 \ln{\left(8 x - 24 \right)}}{8}

    Use \int \frac{k}{x-a}\,dx=k\ln|x-a|.

  14. Combine the integrated terms

    11ln(x3)83ln(x1)4+3ln(x+1)8\frac{11 \ln{\left(x - 3 \right)}}{8} - \frac{3 \ln{\left(x - 1 \right)}}{4} + \frac{3 \ln{\left(x + 1 \right)}}{8}

    Add the logarithmic terms to form the antiderivative.

  15. Select the correct option

    38(x+1)34(x1)+118(x3)\frac{3}{8 \left(x + 1\right)} - \frac{3}{4 \left(x - 1\right)} + \frac{11}{8 \left(x - 3\right)}

    The option matching the constants found is the correct answer.

Answer
38(x+1)34(x1)+118(x3)\frac{3}{8 \left(x + 1\right)} - \frac{3}{4 \left(x - 1\right)} + \frac{11}{8 \left(x - 3\right)}

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