1/a+1/b=1*(1/a+1/b)=(2a+b)*(1/a+1/b)=2+2a/b+b/a+1=3+2a/b+b/a>=3+2(2a/b*b/a)^(1/2)=3+2*2^(1/2)所以1/a+1/b的最小值为3+2*2^(1/2)
