Graph phase portraits for the systems in Prob. 17 with the values of b suggested in the answer. Try to illustrate how the phase portrait changes “continuously” under a continuous change of b.

Data from Prob. 17

The system in Example 4 in Sec. 4.3 has a center as its critical point. Replace each a_jk in Example 4, Sec. 4.3, by a_jk + b. Find values of b such that you get (a) a saddle point, (b) a stable and attractive node, (c) a stable and attractive spiral, (d) an unstable spiral, (e) an unstable node.