x^2-1=3x平方x^4-2x^2+1=9x^2x^4+1=11x^2平方x^8+2x^4+1=121x^4x^8+1=119x^4两边除以x^4x^4+1/x^4=119x^4+1=11x^2两边除以x^2x^2+1/x^2=11(x+1/x)^2=x^2+2+1/x^2=11+2=13x+1/x=±√13