That's a particular case of Jensen's Inequality
Here's a proof I particularly enjoyed reading Art of Problem Solving Forum
And here you have the traditional proof: http://en.wikipedia.org/wiki/Jensen's_inequality
It's a very useful inequality.
That's a particular case of Jensen's Inequality
Here's a proof I particularly enjoyed reading Art of Problem Solving Forum
And here you have the traditional proof: http://en.wikipedia.org/wiki/Jensen's_inequality
It's a very useful inequality.