5.1　向量的概念及运算内容概述1.向量是区别于数量的一种量 ,它由大小和方向两个因素确定 .向量有三种表示法 :一是用有向线段 ,二是用字母 a或 AB,三是用坐标 a =(x,y) .注意共线向量 (也称平行向量 ,方向相同或相反的向量 )与相等向量 (方向相同且模相等 )的联系与区别 .2 . 5.1 Concepts of Vectors and Contents of Operation 1. Vector is a quantity that is different from quantity. It is determined by two factors: size and direction. Vectors have three representations: one is to use directed segments and the other is to use the letters a or AB. The third is to use the coordinates a = (x, y). Note that the collinear vector (also known as the parallel vector, the same or opposite direction of the vector) and the equal vector (the same direction and equal modulus) of the contact and the difference.