设两向量为:向量OA=(x1,y1,z1),向量OB=(x2,y2,z2),它们间的夹角m
则:向量OA*向量OB=x1x2+y1y2+z1z2
而:向量OA*向量OB=|OA|*|OB|cosm
=((x1^2+y1^2+z1^2)(x2^2+y2^2+z2^2))^(1/2)*cosm
cosm=(x1x2+y1y2+z1z2)/((x1^2+y1^2+z1^2)(x2^2+y2^2+z2^2))^(1/2)
m=arccos((x1x2+y1y2+z1z2)/((x1^2+y1^2+z1^2)(x2^2+y2^2+z2^2))^(1/2))