Ответ:

  1. \(\frac{6x(2x-5y)}{6x(5x-2y)}=\frac{2x-5y}{5x-2y}\).
  2. \(\frac{12a(3a+2b)}{12a(2a+3b)}=\frac{3a+2b}{2a+3b}\).
  3. \(\frac{m^2(m-3n)}{3m^2(n-m)}=\frac{3n-m}{3(m-n)}\).
  4. \(\frac{a^2(a-2b)}{-a^3b(a-2b)}=-\frac{1}{ab}\).