明天要交.计算:12/m^2-9+2/3-m；.

你应该是初二的吧
1.12/(m^2-9)+2/(3-m)=12/(m-3)(m+3)-2/(m-3)=12/(m-3)(m+3)-2(m+3)/(m-3)(m+3)
=(6-2m)/(m-3)(m+3)=-2(m-3)/(m-3)(m+3)=-2/(m+3)
2.(x^2-y^2)/(x+y)-[4x(x-y)+y^2]/(2x-y)=(x-y)(x+y)/(x+y)-(4x^2-4xy+y^2)/(2x-y)
=(x-y)-(2x-y)^2/(2x-y)=(x-y)-(2x-y)=y-x