Conditia ca trei puncte sa fie coliniare:
[tex]A(x_A,y_A);\ B(x_B,y_B);\ C(x_C,y_C)\\\\ \frac{y_B-y_A}{x_B-x_A} = \frac{y_C-y_A}{x_C-x_A} [/tex]
[tex] \frac{3-1}{2-1} = \frac{m-1}{3-1}\\
\frac{m-1}{2} =2\rightarrow m-1=4\rightarrow \boxed{m=5} [/tex]
