Question

(a-b)(a-b)(a-b)=a3-3a2b+3ab2+b3

Answer 1

(a-b)(a-b)(a-b) = (a-b)^3
(a-b)^3 = a^3-3a^2b+3ab^2+b^3

Answer 2

(a-b)(a-b)(a-b)= ((a^2-ab-ba-b^2))(a-b)
=a (a^2-2ab+b^2)-b(a^2-2ab+b^2)
=a^3-2a^2b+ab^2-(ba^2-2ab^2
+b^3)
= a^3-3a^2b+3ab^2-b^3.. (proved)