设a,b∈R+,a+2b=3,则1/a+1/b最小值是_.
问题描述:
设a,b∈R+,a+2b=3,则
+1 a
最小值是______. 1 b
答
∵
+1 a
=1 b
(a+2b)(1 3
+1 a
)=1 b
(3+1 3
+2b a
)a b
≥
×21 3
+1
2
∴
+1 a
最小值是1+1 b
2
2
3
故答案为:1+
.2
2
3