Part of CALC-04 — Indefinite Integration

Partial Fractions — Complete Guide

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Prerequisite: Ensure deg(P) < deg(Q). If not, perform polynomial long division first.

Type 1: Distinct Linear Factors Q(x) = (x-a)(x-b)(x-c)... P/Q = Axa\frac{A}{x-a} + Bxb\frac{B}{x-b} + Cxc\frac{C}{x-c} Cover-up method: A = P(a)/[Qx(xa)\frac{x}{(x-a)}] evaluated at x = a.

Type 2: Repeated Linear Factors Q(x) = (x-a)^n P/Q = A1xa\frac{A_1}{x-a} + A2xa\frac{A_2}{x-a}^2 + ... + Anxa\frac{A_n}{x-a}^n Find AnA_n by cover-up at x = a. Find others by comparing coefficients or differentiating.

Type 3: Irreducible Quadratic Factor Q(x) = (x-a)(x2+bx+cx^{2+bx+c}) where x2+bx+cx^{2+bx+c} has no real roots P/Q = Axa\frac{A}{x-a} + Bx+C(x2+bx+c)\frac{Bx+C}{(x^2+bx+c)} The quadratic term integrates to: aln|x2+bx+cx^{2+bx+c}| + barctan form (after completing the square).

Integration After Decomposition:

  • Axa\frac{A}{x-a} integrates to A*ln|x-a|
  • Axa\frac{A}{x-a}^n integrates to A/[(1-n)(x-a)^(n-1)] for n > 1
  • Bx+C(x2+px+q)\frac{Bx+C}{(x^2+px+q)}: split as B2\frac{B}{2}*2x+p(x2+px+q)\frac{2x+p}{(x^2+px+q)} + CBp/2(x2+px+q)\frac{C-Bp/2}{(x^2+px+q)}, giving logarithm + arctan terms

JEE Shortcut for px+q((xa)\frac{px+q}{((x-a)}(x-b)): Write px+q = L(x-a) + M(x-b). Then L = pb+q(ba)\frac{pb+q}{(b-a)}, M = pa+q(ab)\frac{pa+q}{(a-b)}. Integral = Lln|x-a| + Mln|x-b| + C.

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