a^2+b^2=6aba^2+2ab+b^2=8ab(a+b)^2=8aba^2+b^2=6aba^2-2ab+b^2=4ab(a-b)^2=4ab(a+b)^2/(a-b)^2=8ab/4ab=2因为a>b>0所以(a+b)/(a-b)=根号2