Qui peut m'aider a faire le 2 de l'exercice 1 et l'exercice 2 ?

2x - 4y = 7    
5x + 8y = 1

2x - 4y = 7    
2x = 7 + 4y
x = 7/2 + 4y/2

5x + 8y = 1
5(7/2 + 4y/2) + 8y = 1
35/2 + 20y/2 + 8y = 1
 10y + 8y = 1 - 35/2
 18y = 2/2 - 35/2
 18y = - 33/2
 y = - 33/ (2 * 18)
 y = - 33 / (36)
 y = - 11 / 12

x = 7/2 + 4y/2
x = 7/2 + (4/2 * (-11/12))
x = 7/2 + (2 * (-11/12))
x = 7/2 + (1 * (-11/6))
x = 7/2 - 11/6
x = 21/6 - 11/6
x = 10/6
x = 5/3