近几年来,向量越来越被人们所重视.因为向量是沟通代数、几何与三角函数的一种工具,有着极其丰富的实际背景.对某些代数问题,如求函数的最值或值域,如果能巧妙地构造向量,便能将其转化为向量问题.在学习向量的过程中有如下几个结论:(1)由a·b=|a||b|cosθ可知a·b≤|a||b|,当a In recent years, vector has drawn more and more attention because vector is a tool to communicate algebra, geometry and trigonometry, and has extremely rich practical background.For some algebraic problems, such as seeking the most value or range of function , If we can cleverly construct the vector, we can transform it into a vector problem.In the process of learning vector, we can draw the following conclusions: (1) It can be seen from a · b = | a || b | cosθ that a · b≤ | a || b |, when a