孩子问:
x = 1+ x^2
上面两边除x:1 = 1/x +x
两个相加:x+1 = 1 + 1/x +x +x^2
得:0 = 1/x + x^2
得:x^3 = -1, x=-1
代入:x = 1+ x^2, -1=1+(-1)^2=2,
-1=2