(x + 1/x)^2 = x^2 + 2 + 1/(x^2) = 8
故：x^2 + 1/(x^2) = 6
故：(x - 1/x)^2 = x^2 - 2 + 1/(x^2) = 4
所以：x - 1/x = ±2
经验证都符合题意.