d. $(a + b)(a^2 − b^2) + (b − c)(b^2 − c^2) + (c − a)(c^2 − a^2)$
= $(a + b)(a^2 - b^2) - (b - c)[(a^2 - b^2) + (c^2 - a^2)] + (c − a)(c^2 − a^2)$
= $(a + b)(a^2 - b^2) - (b - c)(a^2 - b^2) - (b - c)(c^2 - a^2) + (c − a)(c^2 − a^2)$
= $(a + b - b + c)(a^2 - b^2) + (-b + c + c - a)(c^2 - a^2)$
= $(a + c)(a^2 - b^2) + (-b + c + c - a)((c^2 - a^2)$
= $(a + c)(a^2 - b^2 + (2c - a - b)(c - a))$
e. $a(b + c)^2(b − c) + b(c + a)^2(c−a) + c(a + b)^2(a − b)$
= $a(b + c)^2(b − c) - b(c + a)^2[(b - c) + (a - b)] + c(a + b)^2(a − b)$
= $a(b + c)^2(b − c) - b(c + a)^2(b - c) - b(c + a)^2(a - b) + c(a + b)^2(a − b)$
= $(b - c)[a(b + c)^2 - b(c + a)^2] + [c(a + b)^2 - b(c + a)^2](a - b)$
= $(b - c)(ab^2 + 2abc + ac^2 - a^2b - 2abc - bc^2) + (a^2c + 2abc + b^2c - bc^2 - 2abc - a^2b)(a - b)$
= $(b - c)[ab(b - a) + c^2(a - b)] + [a^2(c - b) + bc(b - c)(a - b)$
= $(b - c)(a - b)(c^2 - ab) + (b - c)(bc - a^2)(a - b)$
= $(a - b)(b - c)[(c^2 - ab) + (bc - a^2)]$
= $(a-b)(b-c)(c-a)(a+b+c)$
$(c^2 - ab) + (bc - a^2)$ vẫn có thể phân tích thành $(c-a).(a+b+c)$