(-1/2m^2-1/3mn+1)·(-1/4m^3n)
=(1/2m^2+1/3mn-1)(1/4m^3n)
=(1/2·1/4)m^(2+3)n+(1/3·1/4)m^(1+3)n^(1+1)-1/4m^3n
=(1/8)m^5n+(1/12)m^4n^2-1/4m^3n
(-1/2m^2-1/3mn+1)·(-1/4m^3n)
=(1/2m^2+1/3mn-1)(1/4m^3n)
=(1/2·1/4)m^(2+3)n+(1/3·1/4)m^(1+3)n^(1+1)-1/4m^3n
=(1/8)m^5n+(1/12)m^4n^2-1/4m^3n