x = t + 1/t
y = t - 1/t
-----------合并
x + y = 2t
t = (x+y)/2
代入 2x = 2t + 2/2t
得到 2x = x + y + 2/(x + y)
整理 x - y = 2 / (x + y)
(x - y)(x + y) = 2
x2 - y2 = 2 ==> x = (2 + y2)1/2 [ 2加上y的平方再开平方]
或者是 y = (x2 - 2)1/2
把t用y表示