(3mn)^2(m^2+mn-n^2)-3mn(3m^3n+3m^2n^2-mn^3)的值
=3m²n²(m^2+mn-n^2)-9m^4n^2-9m^3n^3+6m^2n^4
=3m^4n^2+3m^3n^3-3m^2n^4-9m^4n^2-9m^3n^3+6m^2n^4
=-6m^4n^2-6m^3n^3+3m^2n^4
=-6(-1/4)^4*2^2-6(-1/4)^3*2^3+3(-1/4)^2*2^4
=-3/32+3/4+3
=-75/32