Bonjour,
L/l= 5/3
5 i= 3 L
i = 3 L/5
P= 2(L +l)
120= 2(L + 3L/5)
120= 2L+6L/5
120= (5x2L+6L)/5
120= 16 L/5
16 L= 5x120
L= 600/16
L= 37.5 cm
i = 3 L/5
i= 3(37.5)/5
i= 22.5 cm
Donc A= L x l
A= 37.5 x 22.5
A= 843.75 cm²
Vérification: 2 L +2l= 2(37.5)+2(22.5)= 75+45= 120 cm= P