Binomial Theorem/Abel's Generalisation

Theorem

 * $\displaystyle \left({x + y}\right)^n = \sum_k \binom n k x \left({x - k z}\right)^{k - 1} \left({y + k z}\right)^{n - k}$

for $n \in \Z_{\ge 0}$ and $x \in \R_{\ne 0}$.