(x+1/x)^2=x^2+1/(x^2)+2=9;x^2+1/(x^2)=7;(x-1/x)^2=x^2+1/(x^2)-2=7-2=5则x-1/x＝±√5x^2-1/(x^2)=(x+1/x)(x-1/x)=±3√5
