[tex]\displaystyle\overrightarrow{AM}=4\overrightarrow{MB}\Rightarrow|\overrightarrow{AM}|=4|\overrightarrow{MB}|\Rightarrow AM=4MB\Rightarrow \frac{AM}{MB}=4[/tex]
Din [tex]\displaystyle MN\parallel {BC}[/tex] rezultă [tex]\displaystyle\frac{AN}{NC}=4\Rightarrow CN=\frac{1}{5}AC\Rightarrow\overrightarrow{CN}=\frac{1}{5}\overrightarrow{CA}\Rightarrow m=\frac{1}{5}[/tex]