^2-степень
(mn^3-n^2)×(m-1)

(mn^3 - n^2)(m - 1) = = mn^3(m - 1) - n^2(m - 1) = = m^2n^3 - mn^3 - mn^2 + n^2 = = - mn^3 + n^2 + m^2n^3 - mn^2