Choosing an Integration Technique

Choosing an Integration Technique

Technique selection process for integration.

Techniques of Integration — H2 Mathematics
Standard Integrals from Sec Level
Recognisable Form (Cancelling Method)
Integration of Algebraic fractions
\(\int\dfrac{\mathrm{f}(x)}{\mathrm{g}(x)}\,\mathrm{d}x\quad\text{or}\quad\int\dfrac{\mathrm{f}(x)}{\sqrt{\mathrm{g}(x)}}\,\mathrm{d}x\)
  1. Do long division if the degree of \(\mathrm{f}(x)\) is at least the degree of \(\mathrm{g}(x)\).
  2. If \(\mathrm{f}(x)\) is a constant and \(\mathrm{g}(x)\) is quadratic, complete the square of \(\mathrm{g}(x)\), then use the integrals of
    \(\dfrac{1}{\sqrt{a^2-x^2}},\quad\dfrac{1}{a^2+x^2},\quad\dfrac{1}{a^2-x^2},\quad\dfrac{1}{x^2-a^2}\) in MF 27.
  3. If \(\mathrm{g}(x)\) can be factorised, express \(\dfrac{\mathrm{f}(x)}{\mathrm{g}(x)}\) in partial fractions and integrate.
  4. Lastly, if steps 1–3 are exhausted, consider “Split Up Method”.
    When applicable, let \(\mathrm{f}(x)=A[\mathrm{g}'(x)]+B\), solve for \(A\) and \(B\), then integrate:
    \(\int\dfrac{\mathrm{f}(x)}{\mathrm{g}(x)}\,\mathrm{d}x=\int\Biggl(\underbrace{\dfrac{A\mathrm{g}'(x)}{\mathrm{g}(x)}}_{\substack{\text{Cancelling}\\\text{Method}}}+\underbrace{\dfrac{B}{\mathrm{g}(x)}}_{\text{MF 27}}\Biggr)\mathrm{d}x\)
    or
    \(\int\dfrac{\mathrm{f}(x)}{\sqrt{\mathrm{g}(x)}}\,\mathrm{d}x=\int\Biggl(\underbrace{\dfrac{A\mathrm{g}'(x)}{\sqrt{\mathrm{g}(x)}}}_{\substack{\text{Cancelling}\\\text{Method}}}+\underbrace{\dfrac{B}{\sqrt{\mathrm{g}(x)}}}_{\text{MF 27}}\Biggr)\mathrm{d}x\)

Trigonometric Functions

Use trigonometric identities and change to integrable trigonometric forms or cancelling method. There are 8 trigonometric integrable forms:

  • \(\sin x,\ \cos x,\ \sec^2x,\ \operatorname{cosec}^2x\) [From Sec Level]

  • \(\tan x,\ \cot x,\ \operatorname{cosec}x,\ \sec x\) [From MF 27]

Integration by parts
\(\int u\dfrac{\mathrm{d}v}{\mathrm{d}x}\,\mathrm{d}x=uv-\int v\dfrac{\mathrm{d}u}{\mathrm{d}x}\,\mathrm{d}x\)

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Answer:Choose the simplest valid method in this order: simplify or use a standard integral, try substitution or cancellation, then use an algebraic-fraction or trigonometric transformation, and use integration by parts as a last resort.

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