P=2(L+l)=80, impartim la 2, L+l=40, L=40-l a) L=3l, egalam L, 40-l=3l, l=10 cm, L=30 cm,
b), L=4l, 40-l=4l, 5l=40, l=8 cm, L=32 cm.
c) L=7l, 40-l=7l, 8l=40, l=5 cm, L=35 cm.
d) L=l+20, 40-l=l+20, 2l=40-20=20, l=10 cm, L=30 cm
e) l=2L/3, 3l=2L, L=3l/2, 40-l=3l/2, 80-2l=3l, 5l=80, l=16cm, L=24 cm.