(a – b)3 + (b – c)3 + (c – a)3
= (a – b)3 + (b – c)3 - (a – c)3
= (a – b)3+ (b – c)3 - [(a - b) +(b – c)]3
= (a – b)3+ (b – c)3 - (a – b)3 - 3(a – b)2(b – c) - 3(a – b)(b – c)2- (b – c)3
= - 3 (a – b)(b – c)(a – b)(a - b + b - c)
= 3 (a – b)(b – c)(c - a)