x+3y=-12,4x-6y=-12

x+3y=-12, 2x-3y=-6

x=-3y-12, 2(-3y-12)-3y=-6

x=-3y-12, -6y-24-3y=-6

x=-3y-12, -9y=18

x=-3y-12, y=-2

x=-6-12, y=-2

x=-18, y=-2

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2a-ac-2c+c²=a(2-c)-c(2-c)=(2-c)(a-c)