I would like to know if is possible to access results from a graph. For Eg i have u as a function of r and i would like to plot only the solutions which have real values. In particular the the equation is 0 == u^3 + (b + 2)*u^2 + b*(r + 1)*u + 2*b*(r - 1).
I would like to plot this as I vary r from 0 to 5. The difficulty i am experiencing is that i want to plot only the solutions of u which have no imaginary components. I tried RE[NSolve...] but that also returns the real components of all the complex solutions. I tried playing around using If[Im[sol]=Null,Plot[..],Null] but that doesnt work.
Also, i would like to access the reults once ive plotted them. For example i would like to find u when r is 3. or u when r is 2. I would like to know if i can do this from the graph and would i be able to write these values to another file?