Techniques of Integration · Partial Fractions

Partial Fractions: Distinct Linear

P(x)(xa)(xb)=Axa+Bxb\frac{P(x)}{(x-a)(x-b)} = \frac{A}{x-a} + \frac{B}{x-b}

Decompose a rational function with distinct linear factors in the denominator into simpler fractions that can be integrated individually.

Conditions. Degree of P(x) must be less than the degree of the denominator.
  • 0 variables
  • 2 worked examples
  • 16 in Techniques of Integration

Worked examples

Find ∫ 1/((x-1)(x+2)) dx.
  1. 1/((x-1)(x+2)) = A/(x-1) + B/(x+2)
  2. Multiply through: 1 = A(x+2) + B(x-1)
  3. x = 1: 1 = 3A → A = 1/3. x = -2: 1 = -3B → B = -1/3
  4. ∫ [(1/3)/(x-1) - (1/3)/(x+2)] dx = (1/3)ln|x-1| - (1/3)ln|x+2| + C

Answer: (1/3)ln|(x-1)/(x+2)| + C

1 more worked examplePremium

Find ∫ (5x - 4)/((x - 2)(x + 1)) dx.

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Practice

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