Résoudre chaque système par addition:
a)
-3x + 7y = -15
-6x - 3y = 4
b)
2x + 7y = 9
-3x - 4y = -7
-3x + 7y = -15 / * (-2)
-6x - 3y = 4
6x-14y=30
-6x-3y=4
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0-17y=34
-17y=34
y=-34/17
y=-2
-6x-3y=4
-6x-3(-2)=4
-6x+6=4
-6x=-6+4
x=-2/-6=1/3
x=1/3
y=-2
2x + 7y = 9 /*3
-3x - 4y = -7 /*2
6x+21y=27
-6x-8y=-14
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013y=13
13y=13
y=13/13
y=1
2x+7y=9
2x+7*1=9
2x=9-7
x=2/2
x=1
