Ответ:

  1. \(\frac{a(x+2)}{b(x+2)}=\frac{a}{b}\).
  2. \(\frac{7a+7x}{5a+5x}=\frac{7(a+x)}{5(a+x)}=\frac75\).
  3. Так как \(y-x=-(x-y)\), то \(\frac{3(x-y)}{7(y-x)}=-\frac37\).
  4. \(\frac{3a-6b}{8b-4a}=\frac{3(a-2b)}{4(2b-a)}=-\frac34\).
  5. \(\frac{6ab}{3a+9b}=\frac{6ab}{3(a+3b)}=\frac{2ab}{a+3b}\).
  6. \(\frac{8x^2-4xy}{12x^3}=\frac{4x(2x-y)}{12x^3}=\frac{2x-y}{3x^2}\).

Ответ: а) \(\frac ab\); б) \(\frac75\); в) \(-\frac37\); г) \(-\frac34\); д) \(\frac{2ab}{a+3b}\); е) \(\frac{2x-y}{3x^2}\).