step three.
Draw the arrows on the number line. A right arrow for positive sign and a left arrow for negative sign.
Figure 10. Phase Diagram.
If c is a critical number of
c is a sink if arrows on both side of it point toward it.
c is a source if arrows on both side of it point away from it.
c is a saddle if one arrow points away from and another points toward it.
In Example??, c = 1 is a sink, c = -2,3 are source.
From phase diagram and the sign of derivative of
we can get an very good picture about the behavior of the solutions.
Example 5.2 For x' = f(x) = (x-1)(x+2)(x+3)
which has the following sign distribution,
on intervals
With this information and the phase diagram we have the following picture of typical solutions for x' = (x-1)(x+2)(x-3),