P = 24 cm = 2 × L + 2 × l
Semiperimetrul ( SP ) = P ÷ 2 = 12 cm
SP = l + L
( l = latime , L = lungime )
L = l × 3 => SP = l × 3 + l
SP = 4 l = 12 cm
latimea = 12 cm ÷ 4
lungimea = 3 cm × 3
P = 3 cm × 2 + 9 cm × 2
P = 6 cm + 18 cm
P = 24 cm ( Adevarat )