用完全平方式法（x-1/x）²=（X+1/x）²-4=4则x-1/x的值为正负2
(x+1/x)^2=x^2+1/x^2+2=8 x^2+1/x^2=6(x-1/x)^2=x^2+1/x^2-2=6-2=4x-1/x=2或者-2
解：(x+1/x)^2=8∴x^2+1/x^2+2=8即：x^2+1/x^2=6(x-1/x)^2=x^2+1/x^2-2=4x-1/x=±2
