Réponse :
Cindy a 3 x pin's
Eric a x pin's
Kevin a 3x+5 pin's
3x+x+3x+5 = 89
7x+5=89
7x=89-5
x=12
Cindy a 3 x pin's = 36
Eric a x pin's = 12
Kevin a 3x+5 pin's = 41
1a) P = 4x+20
b) A = (3+x)(7+x)-3*7
A = 21+3x+7x+x²-21
A = x²+10x
2) P = 4x+20 = 38
4x=38-20
x=4,5
A = 4,5²+10*4,8=65,25cm²
Explications étape par étape :
