If a = 7, b = 5 and c = 3, then the value of a2 + b2 + c2

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a² + b² + c² – ab – bc – ca

=	1	[ (a − b)² + (b − c)² + (c − a)²]
	2

=	1	[ (7 − 5)² + (5 − 3)² + (3 − 7)²]
	2

=	1	[ 4 + 4 + 16]
	2

=	1	× 24 = 12
	2