What are some of your favourite integration techniques that are rare or unusual

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Hello could any one tell me some unusual or advanced integration techniques, I am already familiar with the standard ones like u-substitution, integration by parts, trig substitution, partial fractions, Feynman technique (differentiation under the integral), integrating the inverse, Laplace transforms In the integral and matrix inversion so I was wondering if anyone knew some rare ones (definite or indefinite)

Please do not answer with any already listed Otherwise Any help is appreciated Thanks in advance

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Two little known (perhaps?) methods for finding indefinite integrals are:

  1. The Rules of Bioche - Are rules used to guide one towards the most effective trigonometric substitution to use in integrals of the form $$\int f(\sin x, \cos x) \, dx,$$ where $f$ is a rational function of sine and cosine. For more details, see here or here.

  2. Ostrogradsky's Method - Is a method that finds the rational part of $$\int \frac{P(x)}{Q(x)} \, dx,$$ without having to find a factorisation for $Q$ and without having to decompose the integrand into partial fractions. Here $P$ and $Q$ are polynomials such that $\deg P < \deg Q$. For more details, see here.