Răspuns :
L=2l
P=120
P=2x(L+l)=2L+2l
120=2x2l+2l
120=6l
l=120:6
l=20cm
L=2x20
L=40cm
Verificare
2(L+l)=p
2(40+20)=120
2x60=120
120=120
P=120
P=2x(L+l)=2L+2l
120=2x2l+2l
120=6l
l=120:6
l=20cm
L=2x20
L=40cm
Verificare
2(L+l)=p
2(40+20)=120
2x60=120
120=120