Explications étape par étape:
7x - 33 = 6x - 25
7x - 6x = -25 + 33
x = - 25 + 33 = 8cm.
perimétre = 2(7x - 33) + 2AC
80 = 2(56 - 33) + 2AC
80 = 112 - 66 + 2AC
80 = 46 + 2AC
80 - 46 = 2AC
AC = 34/2 = 17cm
Aire = (7x - 33) × AC
= (56 - 33) × 17
= 23 × 17
= 391cm².