平面向量数量积的坐标表示的证明
写出推倒:若向量a=(x1,Y1),b=(x2,y2)则向量a*向量b=x1x2+y1y2的过程?
若向量a=(x1,y1),b=(x2,y2) 则: a*b=x1x2+y1y2的过程? a*b = [a^+b^-(a-b)^]/2 = [(x1^+y1^)+(x2^+y2^)-(x1-x2)^-(y1-y2)^]/2 = x1x2+y1y2
答:两解 设A(x,0),B(0,y) 向量AB=(x,-y),向量AM=(2-x,-3) x=4(2-x),-y=4(-3)得x=8/5,y=12 或x=-4(2...详情>>
答:金师傅!详情>>