Exercice 43 :
a) 4x + 8y = 2
x - 4y = 5
4x + 8y = 2
2x - 8y = 10
4x + 2x + 8y - 8y = 2 + 10
6x = 12
x = 12/6
x = 2
x = 2
4 * 2 + 8y = 2
x = 2
8 + 8y = 2
x = 2
8y = 2 - 8
x = 2
8y = - 6
x = 2
y = - 6/8
x = 2
y = - 3/4
Le couple solution est (2 ; - 3/4).
b) 3a + 2b = 7
4a + 6b = 1
- 9a - 6b = - 21
4a + 6b = 1
- 9a + 4a - 6b + 6b = - 21 + 1
- 5a = - 20
a = - 20 / (- 5)
a = 4
a = 4
3 * 4 + 2b = 7
a = 4
12 + 2b = 7
a = 4
2b = 7 - 12
a = 4
2b = - 5
a = 4
b = - 5/2
Le couple solution est (4 ; - 5/2).
