Weierstrass Substitution

Proof Technique
The Weierstrass substitution is an application of Integration by Substitution.

The substitution is:


 * $u \leftrightarrow \tan \dfrac \theta 2$

for $-\pi < \theta < \pi$, $u \in \R$.

It yields:

Derivative
The above results can be stated:


 * $\ds \int \map F {\sin \theta, \cos \theta} \rd \theta = 2 \int \map F {\frac {2 u} {1 + u^2}, \frac {1 - u^2} {1 + u^2} } \frac {d u} {1 + u^2}$

where $u = \tan \dfrac \theta 2$.

Also see

 * Hyperbolic Tangent Half-Angle Substitution