求高手解一方程

应该是题目错了： x+y+z=9①
x(x+y)=25
z(z+y)=7③
x+y=9-z
z+y=9-x
x(9-z)=25
z(9-x)=7
9x-xz=25
9z-xz=7
x-z=2
代入①得z=(7-y)/2②
将②代入③得（7-y)/2*[(7-y)/2+y]=7
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解得y=√21

哇 你这个方程也够变态的 我用软件算的
x -> 1/7 (42 - 50 (2/(289 - 7 Sqrt[429]))^(1/3) + 625 (2/(289 - 7 Sqrt[429]))^(2/3) + (1/2 (289 - 7 Sqrt[429]))^(2/3) - 2^(2/3) (289 - 7 Sqrt[429])^(1/3)),
y ->
1/42 (154 + 650 (2/(289 - 7 Sqrt[429]))^(1/3) -3750 (2/(289 - 7 Sqrt[429]))^(2/3) +13 2^(2/3) (289 - 7 Sqrt[429])^(1/3) -3 2^(1/3) (289 - 7 Sqrt[429])^(2/3)),
z ->
1/3 (-2 - 25 (2/(289 - 7 Sqrt[429]))^(1/3) - (1/2 (289 - 7 Sqrt[429]))^(1/3))

上面是标准解 Sqrt表示根号 a^b 表示 a的b次方

下面是数值解
{x -> 10.7256, y -> 2.33087, z -> -4.05649}

老哥，要解一元三次方程的，塔尔塔利哑
3个解