设a，b，c∈R，证明：a2+b2+c2≥ab+ac+bc．_刷题宝

题干

设a，b，c∈R，证明：a²+b²+c²≥ab+ac+bc．

上一题下一题 0.0难度选择题更新时间:2012-12-24 06:50:34

答案(点此获取答案解析）

证明：方法一、由a²+b²≥2ab，

a²+c²≥2acb²+c²≥2bc，

相加可得：2a²+2b²+2c²≥2ab+2ac+2bc，

所以a²+b²+c²≥ab+ac+bc（当且仅当a=b=c取得等号）；

<

同类题1

___to complete the job on time, they set out to work immediately.

同类题2

某履带式推土机，其发动机额定功率为120kw，当推土机以额定功率进行推土作业时，在平直的场地上以5.4km/h的速度匀速前进了15m，求：
（1）若推土机的牵引力用F表示，速度用表示，发动机的功率用P表示；请你推导出F、和P之间的关系式：P=F；
（2）推土机受到的阻力是多少？
（3）推土机所做的功是多少？

同类题3

(B)

It's Sunday morning. There are many people in the park.and some boys are playing basketball. There are some girls under a big tree. They're singing and dancing. What are those women doing? They are drinking tea. Look at the woman in a blue coat. Who's she? She's my mother. She is talking to Lin Feng. Lin Feng is her student. He is a good student．He studies hard．He's good at all the subjects. And he's friendly to all his teachers and his friends.

同类题4

像烧杯这样圆柱体形的器皿装上水也具有了放大镜的功能。

同类题5

下列旅游胜地位于越南的是（）

小学学科试题库

初中学科试题库

高中学科试题库