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(a +b +c) ^2 +(a -b) ^2 +(b -c) ^2 +(c - a)^2

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(a +b +c) ^2 +(a -b) ^2 +(b -c) ^2 +(c - a)^2
(a +b +c) ^2 +(a -b) ^2 +(b -c) ^2 +(c - a)^2
(a +b +c) ^2 +(a -b) ^2 +(b -c) ^2 +(c - a)^2
=(a +b +c) ^2 +a²-2ab+b²+b²-2bc+c²+c²-2ac+a²
=(a+b)²+2(a+b)c+c²+2a²+2b²+2c²-2ab-2bc-2ac
=a²+2ab+b²+2ac+2bc+c²+2a²+2b²+2c²-2ab-2bc-2ac
=3a²+3b²+3c²