2012 USAJMO Problems/Problem 3
Contents
[hide]Problem
Let ,
,
be positive real numbers. Prove that
Solution
By the Cauchy-Schwarz inequality,
so
Since
,
Hence,
Again by the Cauchy-Schwarz inequality,
so
Since
,
Hence,
Therefore,
Solution 2
Split up the numerators and multiply both sides of the fraction by either a or 3a:
Then use Titu's Lemma:
It suffices to prove that
After some simplifying, it reduces to
which is trivial by the Rearrangement Inequality. -r31415
See Also
2012 USAJMO (Problems • Resources) | ||
Preceded by Problem 2 |
Followed by Problem 4 | |
1 • 2 • 3 • 4 • 5 • 6 | ||
All USAJMO Problems and Solutions |