5. \(\frac{6(x-y)}{12z(y-x)}\)

Так как \(y-x=-(x-y)\), получаем:

\[\frac{6(x-y)}{12z(y-x)}=\frac{6(x-y)}{-12z(x-y)}=-\frac1{2z}.\]

Ответ: \(-\frac1{2z}\)