In calculus, a technique of integration is a method of evaluating a relatively difficult integral, usually by rewriting it in a simpler form. Common techniques of integration include: * Integration by substitution ("u-substitution" in two dimensions or coordinate transformation by means of a Jacobian matrix in multivariable calculus) * Integration by parts * Integration by partial fractions * Integration by trigonometric substitution * Approximation (by Taylor series or Riemann sum)