a方-3a+1=0 两边同时除以a得 a+1/a=3 两边同时平方得 a^2+1/(a^2)+2=9 a^2+1/(a^2)=7 1/a+1/b=6/(a+b) (a+b)/ab=6/(a+b) (a+b)^2=6ab a^2+2ab+b^2=6ab a^2+b^2=4ab (a^2+b^2)/ab=4 a/b+b/a=4
