partial sum的用法和樣例：
例句
- The infinite series diverges, meaning that its sequence of partial sums does not tend towards any finite limit.Equivalently, one says that lacks a sum.
此無窮級數發散，即其部分和的序列不會趨近於任一有窮極限，可等價地認為不存在和。 - Up to a certain sum of the interior angles on one side of the transversal the two lines might indeed meet.
截線一側兩內角到達一定的和數，兩直線可能一定相交。 - The greater the sum, the greater the cross-correlation coefficient obtained in this way will be.
和數越大，以這種形式得到的相關係數也越大。
