Question 910254
Proof of what?
Do you mean you want the expansion?
{{{(a+b)^3=(a+b)^2(a+b)}}}
{{{(a+b)^3=a(a+b)^2+b(a+b)^2}}}
So,
{{{(a+b)^2=(a+b)(a+b)}}}
{{{(a+b)^2=a(a+b)+b(a+b)}}}
{{{(a+b)^2=(a^2+ab)+(ab+b^2)}}}
{{{(a+b)^2=a^2+2ab+b^2}}}
So then,
{{{(a+b)^3=a(a+b)^2+b(a+b)^2}}}
{{{(a+b)^3=a(a^2+2ab+b^2)+b(a^2+2ab+b^2)}}}
{{{(a+b)^3=(a^3+2a^2b+ab^2)+(a^2b+2ab^2+b^3)}}}
{{{(a+b)^3=a^3+3a^2b+3ab^2+b^3}}}