Résoudre chaque système par la combinaison Quelqu'un saurait m'aider svp?

- x + 10y = - 1
2x + 5y = 8

- x = - 1 - 10y
x = 1 + 10y

2x + 5y = 8
2 (1 + 10y) + 5y = 8
2 + 20y + 5y = 8
20y + 5y = 8 - 2
25y = 6
y = 6/25

x = 1 + 10y
x = 1 + 10 * 6/25
x = 1 + 60/25
x = 1 + 2,4
x = 3,4

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2x - 9y = 3
- 10x + 7y = - 4

14x - 63y = 21
- 90x + 63y = - 36
- 76x = - 36
x = 36/76
x = 9/19

2x - 9y = 3
2 * 9/19 - 9y = 3
18/19 - 9y = 3
- 9y = 3 - 18/19
- 171/19y = 57/19 - 18/19
- 171/19y = 39/19
- 171y = 39
y = - 39/171
y = - 13/57

Exercice 71 :

B-
- x + 10y = - 1
2x + 5y = 8

- x = - 1 - 10y
2x + 5y = 8

x = 1 + 10y
2x + 5y = 8


x = 1 + 10y
2 (1 + 10y) + 5y = 8

x = 1 + 10y
2 + 20y + 5y = 8

x = 1 + 10y
25y = 8 - 2

x = 1 + 10y
25y = 6

x = 1 + 10y
y =6/25


x = 1 + 10y
y =6/25

x = 1 +10(6/25)
y =6/25


x = 1 + 60/25
y =6/25

x = 25/25 + 60/25
y =6/25

x = 85/25
y = 6/25

x = 17/5
y = 6/25






Exercice 72 :

B-

2x - 9y = 3
-10x + 7y = -4

x - 4,5y = 1,5
-10x + 7y = -4

x = 1,5 + 4,5y
-10x + 7y = -4

x = 1,5 + 4,5y
-10(1,5 + 4,5y) + 7y = -4

x = 1,5 + 4,5y
-15 - 45y + 7y = -4

x = 1,5 + 4,5y
- 38y = - 4 + 15

x = 1,5 + 4,5y
- 38y = 11

x = 1,5 + 4,5y
y = -11/38


x = 1,5 + 4,5(-11/38)
y = -11/38

x = 1,5 - 49,5/38
y = -11/38


x = 57/38 - 49,5/38
y = -11/38


x = 7,5/38
y = -11/38

x = 75/380
y = -11/38

x = 15/76
y = -11/38