已知a向量=(x1,y1-1),b向量=(x2,y2-2),则a向量*b向量等于?
问题描述：
已知a向量=(x1,y1-1),b向量=(x2,y2-2),则a向量*b向量等于?
答
a·b=(x1,y1-1)·(x2,y2-2)
=x1x2+(y1-1)(y2-2)
=x1x2+y1y2+2-2y1-y2题目打错了，是y2-1a·b=(x1,y1-1)·(x2,y2-1)=x1x2+(y1-1)(y2-1)=x1x2+y1y2+1-y1-y2