Réponses

2014-10-10T21:32:18+02:00
X1+x2+x3=5 (1)
x1-x2+x3=3 (2)
2x1-x2-x3=1 (3)

(1)-(2)=> x1+x2+x3-x1+x2-x3=5-3
=> 2x2=2 => x2=2/2=1

(1)+(3)=> x1+x2+x3+2x1-x2-x3=5+1
=> 3x1=6. => x1=6/3=2

on remplace x1 et x2 dans (1)
2+1+x3=5
x3=5-3=2

x1=2
x2=1
x3=2