Note that , so one has to show that . After multiplying both sides by 3 and moving everything to the left, that expression can be represented as a sum of two squares.
Note that , so one has to show that . After multiplying both sides by 3 and moving everything to the left, that expression can be represented as a sum of two squares.
Maybe I have a blind spot, but I don't see that last step of getting to the sum of two squares. Is there some identity that I've forgotten ? .
I can get to the result using the AM >= GM inequality, (so