又|=x+y+zk F=Fi+F i+Fk 则」M(F)=(xF)=(x2++z6)x(F+F,+F) FFF (F -zF)i+(zF -xF)j+(xF-yF)k 力对0点的矩在三个坐标轴的投影: Mo(F) M(F)I=VF-2F 7A(r, a M(F)I=ZF-xF M(F)I=xF-yF又 则 力对O点的矩在三个坐标轴的投影：