Theorem T59 (x+y)r=∑k=0r(rk)xkyr−k(x + y)^r = \sum_{k=0}^r \binom{r}{k} x^k y^{r - k} (x+y)r=k=0∑r(kr)xkyr−k for integer r≥0r \geq 0r≥0. notation-integer-finite-summation