Part of CALC-10 — Integration: Advanced Techniques & Reduction

Partial Fraction Decomposition — Complete Method

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When to use: Integrating PxQ\frac{x}{Q}(x) where Q(x) factors into linear and quadratic terms.

Step 1: If deg(P) >= deg(Q), divide first to get polynomial + proper fraction.

Step 2: Factor Q(x) completely over the reals.

Step 3: Write the decomposition:

  • Each factor (x-a) contributes Axa\frac{A}{x-a}
  • Each factor (x-a)^k contributes A1xa\frac{A1}{x-a} + A2xa\frac{A2}{x-a}^2 + ... + Akxa\frac{Ak}{x-a}^k
  • Each factor (x2+px+qx^{2+px+q}) contributes Ax+B(x2+px+q)\frac{Ax+B}{(x^2+px+q)}
  • Repeated quadratic factors: similar stacking

Step 4: Find coefficients by:

  • Substituting roots of Q (cover-up method for distinct linear factors)
  • Comparing coefficients of powers of x
  • Using convenient values of x

Step 5: Integrate each term:

  • Axa\frac{A}{x-a} => A*ln|x-a|
  • Axa\frac{A}{x-a}^n => A(x-a)^1n(1n)\frac{1-n}{(1-n)}
  • Ax+B(x2+px+q)\frac{Ax+B}{(x^2+px+q)} => split into ln and arctan parts

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