4) \(\dfrac{c-1}{c+2}-\dfrac{c-2}{c+1}\)

Общий знаменатель: \((c+2)(c+1)\).

\[\dfrac{c-1}{c+2}-\dfrac{c-2}{c+1}=\dfrac{(c-1)(c+1)-(c-2)(c+2)}{(c+2)(c+1)}.\]

Раскроем скобки:

\[\dfrac{c^2-1-(c^2-4)}{(c+2)(c+1)}=\dfrac{3}{(c+2)(c+1)}.\]

ОДЗ: \(c\ne-2\), \(c\ne-1\).

Ответ: \(\dfrac{3}{(c+2)(c+1)}\).