b)a(b-c)3+b(c-a)3+c(a-b)3
Bạn tự tách trong ngoặc ra nhá
=ab3-ac3+bc3-a3b+a3c-b3c
=b3(a-c)+ac(a2-c2)-b(a3-c3)
=b3(a-c)+ac(a-c)(a+c)-b(a-c)(a2+ac+c2)
=(a-c)[b3+ac(a+c)-b(a2+ac+c2)]
=(a-c)(b3+a2c+ac2-ba2-abc-bc2)
=(a-c)[ac(a+c)+b(b2-a2)-bc(a+c)]
=(a-c)[c(a+c)(a-b)-b(a-b)(a+b)]
=(a-c)(ca+c2-ab-b2)(a-b)