点M∈丌<PM,C1,a2共面 oPM=t,a,+t,a 仿射坐标系{O;e1,e2,e3} 给定P:(x0,Jn,),ax1:(x1,n1,x1), 设M:(x,y,x) PM: x-xo,v-y0,4 0