> [!theorem] > > Let $\bracs{x_n}$ and $\bracs{y_n}$ be [[Sequence|sequences]], then > $ > \sum_{k = m}^{n}x_k(y_{k + 1} - y_k) = (x_{n+1}y_{n+1} - x_my_m) - \sum_{k = m}^{n}y_{k + 1}(x_{k + 1} - x_k) > $