2lg(x-y)/2=lgx+lgy
(x+y)^2/4=x*y 两者都除以y^2
得 (x/y)^2-6*x/y+1=0
x/y=3+2√2或x/y=3-2√2
当x/y=3+2√2时,log以(3-2√2)为底,x/y的值=log(3-2√2)[3+2√2]
当x/y=3-2√2时,log以(3-2√2)为底,x/y的值=1