作业帮3x+3y=-3 x(x+y)(x+2y)=-8 求x,y
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3x+3y=-3 x(x+y)(x+2y)=-8 求x,y
3x+3y=-3 x(x+y)(x+2y)=8
3x+3y=-3 x(x+y)(x+2y)=8
∵ 3 x + 3 y = - 3
∴ x + y = - 1
∴ y = - 1 - x
∴ x（x + y）（x + 2 y）= 8 【把 y = - 1 - x 代入】
x（x - 1 - x）（x - 2 - 2 x）= 8
x ·（- 1）（- 2 - x）= 8
x（x + 2）= 8
x ² + 2 x = 8
x ² + 2 x + 1 = 9
（x + 1）²= 9
x + 1 = ± 3
x = ± 3 - 1
x1 = 3 - 1 = 2
x2 = - 3 - 1 = - 4
①当 x = 2 时,则 y = - 1 - 2 = - 3
② 当 x = - 4 时,则 y = - 1 -（- 4）= - 1 + 4 = 3
∴ x + y = - 1
∴ y = - 1 - x
∴ x（x + y）（x + 2 y）= 8 【把 y = - 1 - x 代入】
x（x - 1 - x）（x - 2 - 2 x）= 8
x ·（- 1）（- 2 - x）= 8
x（x + 2）= 8
x ² + 2 x = 8
x ² + 2 x + 1 = 9
（x + 1）²= 9
x + 1 = ± 3
x = ± 3 - 1
x1 = 3 - 1 = 2
x2 = - 3 - 1 = - 4
①当 x = 2 时,则 y = - 1 - 2 = - 3
② 当 x = - 4 时,则 y = - 1 -（- 4）= - 1 + 4 = 3
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