Chapter D1.4, Problem 21E

Stability of equilibrium points Find the equilibrium solution of the following equations, make a sketch of the direction field, for t ≥ 0, and determine whether the equilibrium solution is stable. The direction field needs to indicate only whether solutions are increasing or decreasing on either side of the equilibrium solution.

21.     $u^{\prime }\left(t\right)+7u+21=0$