Résous les systèmes suivants en utilisant la méthode par combinaisons.
B. 3x + 5y = 2
5x + 2y = -1
C. 2x - 5y = -1
3x + 7y = 4
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B. 3x + 5y = 2
5x + 2y = -1
C. 2x - 5y = -1
3x + 7y = 4
Je ne comprend vraiment rien!!
Merci d'avance
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(5x + 2y = -1) x-3
= 15x + 25y = 10
-15x -6y = 3
= 19y = 13
y = 19/13
que tu remplaces dans 5x + 2(19/13)= -1
5x + 38/13 = -1
5x = -1 - 38/13
5x= -52/13
x = -52/ 65
C. (2x -5y = -1) x3
(3x + 7y = 4) x-2
= 6x -15y = -3
-6x - 14 y = -8
= -29y= -11
y= 11/29
On remplace y dans 2x- 5y =-1
2x -5(11/29)= -1
2x - 55/29 = -1
2x= 26/29
x = 26/58 = 13/29
5x + 2y = -1 3* (5x+2y) = 3*-1
15x+25y = 10 15x + 25 y = 10
15x+6y = -3 15x+25y - (15x+6y) = 10 -(-3)
15x+25y = 10 15x+25y = 10
15x+25y-15x-6y = 10+3 9y=13
15x+25y= 10 15x+25*13/9 = 10 x = (10-25*13/9)/15
y = 13/9 y = 13/9 y = 13/9
x = -235/135
y= 13/9
C. 2x - 5y = -1 3*(2x-5y) = 2*-1 6x-15y = -2
3x + 7y = 4 2*(3x+7y)= 2*4 6x+14y = 8
6x-15y = -2 6x-15y = -2
6x-15y -(6x+14y)=-2-8 6x-15y-6x-14y = -10
6x -15 y = -2 6x-15y = -2 6x - 15 *10/29 =- 2
-29y = -10 y = 10/29 y= 10/29
x= ( -2 +15*10/29)/6 x = 92/174 = 46/87
y=10/29 y= 10/29 = 10/29