b-1/a-1可以看成動(dòng)點(diǎn)P與定點(diǎn)Q（1,1） 兩點(diǎn)之間的斜率,所以求斜率的取值范圍
kAQ=(4-1)/(2-1)=3
kBQ=(3-1)/(3-1)=1
所以 b-1/a-1的取值范圍為 1???????ABC?С?A(m ,2)??B(-3,-??,C??5,1??????BC???е?M??AB????????M??AC?????,?????m??????Χ?????AB????????????y=3x/(m+3)+(6-m)/(m+3)AC???????????y=-5x/(5-m)+(10-m)/(5-m)M??????M(1,0)M??AB????=|9-m|/??[9+(m+3)^2]M??AC????=|5-m|/??[25+(5-m)^2]??M??AB????????M??AC????????????|9-m|>|5-m|m<7?????????????????????m??????Χ?m<7??