A(2,3)B(3,-2)C(1/2,m) 三点共线
则
Kab=Kac
(-2-3)/(3-2)=(m-3)/(1/2-2)
-5=(m-3)/ -3/2
m-3=-5*(-3/2)=15/2
m=3+15/2=21/2