Ответ:

  1. \(\frac{m((m+n)-n)}{n(m+n)}=\frac{m^2}{n(m+n)}\).
  2. \(\frac{a(a+3)-3(a-3)}{a^2-9}=\frac{a^2+9}{a^2-9}\).
  3. \(\frac{2c}{9c^2-1}\).
  4. \(\frac{x((3y-2)-(2y+1))}{(2y+1)(3y-2)}=\frac{x(y-3)}{(2y+1)(3y-2)}\).