Algebra 2 (1st Edition)

$(a-b)^3=(a-b)(a-b)(a-b)=(a^2-ab-ab+b^2)(a-b)=(a^2-2ab+b^2)(a-b)=a^3-2a^2b+b^2a-a^2b+2ab^2-b^3=a^3-3a^2b+3ab^2-b^3$ Thus we proved what we had to.