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

Integration of 1/(ax^2+bx+c) — General Method

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Method: Complete the square in the denominator to reduce to standard forms.

ax2ax^2 + bx + c = a[(x + b2a\frac{b}{2a})^2 + (c/a - b^24a2\frac{2}{4a^2})]

Case 1: Discriminant < 0 (no real roots) Integral = 1a\frac{1}{a} * 1k\frac{1}{k} * arctan((x+b2a\frac{b}{2a})/k) where k2k^2 = ca\frac{c}{a} - b^24a2\frac{2}{4a^2}

Case 2: Discriminant > 0 (real roots) Factor into (x-r1)(x-r2) and use partial fractions: Axr1\frac{A}{x-r1} + Bxr2\frac{B}{x-r2}

Case 3: Perfect square (discriminant = 0) Integral = -1a(x+b/(2a\frac{1}{a(x+b/(2a})) + C

Important standard results:

  • integral dxx2+a2\frac{dx}{x^2+a^2} = 1a\frac{1}{a}arctanxa\frac{x}{a} + C
  • integral dxx2a2\frac{dx}{x^2-a^2} = 12a\frac{1}{2a}ln|xa(x+a)\frac{x-a}{(x+a)}| + C

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