[tex] \left \{ {{ \frac{AB}{3} = \frac{AC}{4} } \atop {AB+BC+AC=72}} \right. \ \textless \ =\ \textgreater \ \left \{ {{AB= \frac{3AC}{4} } \atop {BC+\frac{3AC}{4} +AC=72}} \right. \ \textless \ =\ \textgreater \ BC=72- \frac{7AC}{4} [/tex]
BC²=AB²+AC²
BC²=[tex] \frac{9}{16} [/tex]AC²+AC²
BC²=[tex] \frac{25}{16} [/tex]AC²=[tex] \frac{5}{4} [/tex]AC
Egalam partile
[tex] \frac{5}{4} [/tex]AC=72-[tex] \frac{7}{4} [/tex]AC
3AC=72
AC=24 cm
BC=[tex] \frac{5}{4} [/tex]*24=30 cm