Theorem T60 (x+y)r=∑k∈Z(rk)xkyr−k(x + y)^r = \sum_{k \in \mathbb{Z}} \binom{r}{k} x^k y^{r - k} (x+y)r=k∈Z∑(kr)xkyr−k for real rrr and ∣x/y∣<1\mathopen| x / y \mathclose| < 1∣x/y∣<1. notation-real-infinite-summation