Problem:
If are non-negative real numbers with sum equal to then find the maximum value of the expression
Solution:
First we may, without loss of generality, assume that Now, we shall prove that
It holds that
Therefore, we only need to prove that
For we get
or equivalently the above Inequality reduces to the But this one holds due to the AM-GM Inequality since we have
Now, for on the other side, we only need to show that
or
But, again, from the AM-GM Inequality we acquire
So, finally, we are left to find the maximum value of the expression
We have according to the AM-GM Inequality
Thus, the maximum value of the expression is equal to and it is obtained if and only if Q.E.D.