\[- 28;x_{2};x_{3};x_{4};12;\ldots\]
\[x_{1} = - 28;\ \ x_{5} = 12;\]
\[x_{5} = x_{1} + 4d\]
\[12 = - 28 + 4d\]
\[4d = 40\]
\[d = 10.\]
\[x_{2} = x_{1} + d = - 28 + 10 = - 18;\]
\[x_{3} = x_{2} + d = - 18 + 10 = - 8;\]
\[x_{4} = x_{3} + d = - 8 + 10 = 2.\]
\[Ответ:\ - 18;\ - 8;2.\]