Trigonometric Integrals Using Identities

Trigonometric Integrals Using Identities

Use an identity to rewrite each squared trigonometric function as a sum of standard integrable terms.

Squared sine and cosine

IntegralIdentity and rewriteAntiderivative
\(\displaystyle\int\sin^2x\,\mathrm{d}x\)\(\sin^2x=\dfrac{1-\cos2x}{2}\)\(\dfrac{x}{2}-\dfrac{\sin2x}{4}+C\)
\(\displaystyle\int\cos^2x\,\mathrm{d}x\)\(\cos^2x=\dfrac{1+\cos2x}{2}\)\(\dfrac{x}{2}+\dfrac{\sin2x}{4}+C\)

Squared tangent and cotangent

IntegralIdentity and rewriteAntiderivative
\(\displaystyle\int\tan^2x\,\mathrm{d}x\)\(\tan^2x=\sec^2x-1\)\(\tan x-x+C\)
\(\displaystyle\int\cot^2x\,\mathrm{d}x\)\(\cot^2x=\mathrm{cosec}^2x-1\)\(-\cot x-x+C\)
Identity check

\[\cos2A=1-2\sin^2A=2\cos^2A-1\]

  • Rewrite before integrating.
  • Integrate each standard term separately.
  • Differentiate the result to check the identity and signs.

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