a+2b=1,求1/a+1/b的最值是吗?
1/a+1/b=1*(1/a+1/b)=(a+2b)*(1/a+1/b)=1+2+a/b+2b/a
应用均值不等式的1+2+a/b+2b/a≥1+2+2根号(a/b*2b/a)=3+2根号2