O(n³)

double a[N][N];//增广矩阵

int gauss()
{
    int c, r;
    for (c = 0, r = 0; c < n; c++)
    {
        int t = r;
        for (int i = r; i < n; i++)//寻找首位绝对值最大的行
        {
            if (fabs(a[i][c]) > fabs(a[t][c]))
            {
                t = i;
            }
        }
        if (fabs(a[t][c]) < 1e-6)
        {
            continue;
        }
        for (int i = c; i <= n; i++)//将首位绝对值最大的行换到最顶端
        {
            swap(a[t][i], a[r][i]);
        }
        for (int i = n; i >= c; i--)//将当前行的首位变成1
        {
            a[r][i] /= a[r][c];
        }
        for (int i = r + 1; i < n; i++)//用当前行将下面所有的列消成0
        {
            if (fabs(a[i][c]) > 1e-6)
            {
                for (int j = n; j >= c; j--)
                {
                    a[i][j] -= a[r][j] * a[i][c];
                }
            }
        }
        r++;
    }
    if (r < n)//矩阵不满秩
    {
        for (int i = r; i < n; i++)
        {
            if (fabs(a[i][n]) > 1e-6)
            {
                return 2;//无解
            }
        }
        return 1;//无穷多解
    }
    for (int i = n - 1; i >= 0; i--)
    {
        for (int j = i + 1; j < n; j++)
        {
            a[i][n] -= a[i][j] * a[j][n];
        }
        if(fabs(a[i][n])<1e-6)//防止精度问题输出-0.00
        {
            a[i][n]=0;
        }
    }
    return 0;//有唯一解
}

for (int i = 0; i < n; i++)
{
    for (int j = 0; j < n + 1; j++)
    {
        scanf("%lf", &a[i][j]);
    }
}

for (int i = 0; i < n; i++) //res
{
    printf("%.2lf\n", a[i][n]);
}