在直角坐标系内,已知两点P1(x1,y1),P2(x2,y2);在→P1P2所在直线上有一异于P2的点P,设它的坐标为(x,y),那么λ=→P1P/→PP2=(P-P1)/(P2-P)=[(x,y)-(x1,y1)]/[(x2,y2)-(x,y)]=(x-x1,y-y1)/(x2-x,y2-y)(x-x1)/(x2-x) -  - (1)={(y-y1)/(y2-y) -  - (2).在直角坐标系内,已知两点P1(x ,y ),P2(x ,y ); 在→P1P2所在直线上有一异于P2的点P,设它的坐标为(x,y), 那么λ=→P P→PP =(P-P )(P -P) =[(x,y)-(x ,y )][(x ,y )-(x,y)] =(x-x ,y-y )(x -x,y -y) (x-x )(x -x)  -  - (1) ={ (y-y )(y -y)  -  - (2) 注:→P1P表示"向量P1P" 则λ称为点P分→P1P的比,它是实数,取值范围为R;