Question

Folks,
I have a question about stable vs unstable points of equilibrium in a phase field. This is from the tail end of a calculus 2 course (not difeq) We are solving these graphically. The directions state to find the point of equilibrium and determine which are stable and which are unstable. I realize that if there is a concavity change, one of the points become unstable. I'm having a hard time determining which one. On the attached picture I've shown my work, I'd like to know if any of you have any pointers on how to determine the stability. See attached image