X 為正數(shù)時（X不為0）可以知道
X=1/(1-X)
X-X^2=1 兩邊除X
1=X+1/X
1/x+x的值為1
X為負(fù)數(shù)
X=-1/(1-X)
X-X^2=-1
1=X-1/X
兩邊平方
1=X^2+1/X^2-2
X^2+1/X^2=3
(1/x+x)^2=X^2+1/X^2+2=5
1/x+x的值-5^0.5 應(yīng)為X為負(fù)數(shù)
答案是 1或-5^0.5