x/(xx+x+1)=a分子分母除以x,1/(x+1+1/x)=a,x+1/x=1/a -1,两边平方xx +2+ 1/xx=(1/a-1)^2xx+ 1/xx=(1/a-1)^2-2xx/(xxxx+xx+1)分子分母除以xx=1/(xx+1/xx+1)=1/〔(1/a-1)^2-2+1〕=1/〔(1/a-1)^2-1〕=a^2/(1-2a) ....