Question 250828
{{{(a-3b)^4}}}


{{{(a-3b)^2(a-3b)^2}}}


{{{(a-3b)(a-3b)(a-3b)^2}}}


{{{(a^2-3ab-3ab+9b)(a-3b)^2}}}


{{{(a^2-6ab+9b)(a^2-6ab+9b)}}}


{{{a^4-6a^3b+9a^2b-6a^3b+36a^2b^2-54ab^2+9a^2b-54ab^2+81b^2}}}


Now combine like terms:
{{{a^4-6a^3b-6a^3b+9a^2b+9a^2b+36a^2b^2-54ab^2-54ab^2+81b^2}}}


{{{a^4-12a^3b+18a^2b+36a^2b^2-108ab^2+81b^2}}}