Question 34440
the answer you get is wrong. It should do like this
{{{m^2+n^2-mn)(m^2+mn+n^2)}}}
= {{{m^2(m^2+mn+n^2) + m^2(m^2+mn+n^2)- mn(m^2+mn+n^2)}}}
= {{{m^4 + m^2n + m^2n^2 + n^2m^2 + mn^2 + n^4 - m^3n - m^2n^2 - mn^3}}}
that your answer. Does the problem told you to collect like terms? If so, then the answer should turn to be like this: {{{m^4 + n^2m^2 + n^4}}}