So, we want to decompose the position vector into a sumof simpler vectors.
故我们是把位置向量，分解为简单向量的和。
2
Only if the component vectors are on a straight line will the length of the vector for the sum be equal to the sum of the lengths of these components or to their difference.
只有当几个分矢量在一直线上，那么表示其和的矢量长度才会等于这些分量的长度和或它们的差。
3
The operation of finding the sumof two vectors is called vector addition .