>>747
3(a^2+b^2+c^2) - (a+b+c)^2
= 2(a^2+b^2+c^2) - 2(ab+bc+ca)
= (a^2 - 2ab + b^2) + )b^2 - 2bc + c^2) + (c^2 - 2ca + a^2)