comment résoudre ce système sachant que la réponse est a=3 et b=2 : 13a+11b+15x5=13,6x(a+b+5) 15a+17b+14x5=14,9x(a+b+5)

bonsoir

13 a + 11 b + 75 = 13.6 a + 13.6 b + 68
13 a - 13.6 a + 11 b - 13.6 b = 68 - 75
- 0.6 a - 2.6 b = - 7

15 a + 17 b + 70 = 14.9 a + 14.9 b + 74.5
15 a- 14.9 a + 17 b - 14.9 b = 74. 5 - 70
0.1 a + 2.1 b = 4.5

- 0.6 a - 2.6 b = - 7
0.1 a + 2.1 b = 4.5

- 0.6 a - 2.6 b = - 7
   0.6 a + 12.6 b = 27

10 b = 20
b = 2

- 0.6 a - 5.2 = - 7
- 0.6 a = - 7+ 5.2
- 0.6 a = 1.8
a = 3