（X-1)/(X-3)=3-M/(3-X)（X-1)/(X-3)-M/(3-X)=3(X-1-M)/(X-3)=3X-1-M=3X-9 2X=8-MX=4-(1/2)M4-(1/2)M=3M=2
答案是不是2呀
