(a−b)3+(b−c)3+(c−a)3=3(a−b)(b−c)(c−a)
(a - b)3 + (b - c)3 + (c - a)3
= a3 - 3a2b + 3ab2 - b3 + b3 - 3b2c + 3bc2 - c3 + c3 - 3ac2 + 3a2c - a3
= (a3 - a3) + (b3 - b3) + (c3 - c3) - 3(a2b + ac2 - ab2 - bc2 + b2c - a2c)
= 3[(a2b - ab2) + (ac2 - bc2) - (a2c - b2c)]
= 3[ab(a - b) + c2(a - b) - c(a2 - b2)]
= 3[ab(a - b) + c2(a - b) - c(a + b)(a - b)]
= 3(a - b)[ab + c2 - c(a + b)]
= 3(a - b)(ab + c2 - ac - bc)
= 3(a - b)[(ab - ac) - (bc - c2)]
= 3(a - b)[a(b - c) - c(b - c)]
= 3(a - b)(a - c)(b - c)