bonsoir,
On pose AM = x cm
Périmètre petit rectangle = 2 ( x + 2 ) = 2 x + 4
Périmètre grand rectangle = 2 ( 15 - x + 3 ) = 30 - 2 x + 6 = - 2 x + 36
2 x + 4 = - 2 x + 36
2 x + 2 x = 36 - 4
4 x = 28
x = 7
il faut que AM mesure 7 cm
Aire petit rectangle = 2 x
Aire grand rectangle = ( 15 - x ) ( 3) = 45 - 3 x
- 3 x + 45 = 2 x
- 3 x - 2 x = - 45
- 5 x = - 45
x = 9