bc(b + c) + ca(c - a) - ab(a + b) = b2c + bc2 + c2a - ca2 - ab(a + b) = (b2c - a2c) + (bc2 + ac2) - ab(a + b)
= c(b - a)(b + a) + c2(b + a) - ab(a + b) = (a + b)[c(b - a) + c2 - ab] = (a + b)[(cb - ab) + (c2 - ca)]
= (a + b)[b(c - a) + c(c - a)] = (a + b)(b + c)(c - a)