Réponses

2014-09-07T18:34:07+02:00
Bonjour,
pas évident!!!
1: u=3/2a+b

2:
a=2x+y (1)
b=x+3y (2)
u=-4x+3y

(1) et (2)=>x=3/5a-b/5 , y=-a/5+2b/5
=>u=-4*(3/5a-b/5)+3*(-a/5+2b/5)=-3a+2b.