Ответ:

а) \(\frac{16x^3y}{20x^2y^2}=\frac{4x}{5y}\).

б) \(\frac{a^2-ab}{a^2}=\frac{a(a-b)}{a^2}=\frac{a-b}{a}\).

в) \(\frac{m^2-n^2}{mn+n^2}=\frac{(m-n)(m+n)}{n(m+n)}=\frac{m-n}{n}\).

г) \(\frac{c^2+c}{c^2-c}=\frac{c(c+1)}{c(c-1)}=\frac{c+1}{c-1}\).

д) \(\frac{z-1}{a-az}=\frac{z-1}{a(1-z)}=\frac{z-1}{-a(z-1)}=-\frac{1}{a}\).

Ответ: а) \(\frac{4x}{5y}\); б) \(\frac{a-b}{a}\); в) \(\frac{m-n}{n}\); г) \(\frac{c+1}{c-1}\); д) \(-\frac{1}{a}\).