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Let . ,and such that and inequality to prove become
, similarly:
Now the requirement that x+y+z = 0 guarantees that for (x,y,z) one has (0,0,0) (0, +, - ) (+,+,-) or (+, - , - ) as positive/negative quantities for the triple! Thus atleast one of xy,xz, or yz has a product which is positive!
Finally, the triangle inequality ensures the following: a+b>c, a+c>b, and b+c>a Combining all the above assures us that at least one of the above representations for Q is the sum of two positive quantities.
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