Square of a plus square of B plus square of C minus AB minus AC minus BC minus AC

Square of a plus square of B plus square of C minus AB minus AC minus BC minus AC

a²+b²+c²-ab-bc-ac
=(1/2)[(a²-2ab+b²)+(b²-2bc+c²)+(c²-2ac+a²)]
=(1/2)[(a-b)²+(b-c)²+(c-a)²]
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