I keep having problems using sage. When I get to the part where I have to plot, I get the following message and the plot comes out completely blank:
__main__:4: DeprecationWarning: Substitution using function-call syntax and unnamed arguments is deprecated and will be removed from a future release of Sage; you can use named arguments instead, like EXPR(x=…, y=…) See http://trac.sagemath.org/5930 for details.
I am having the same issue with both, problem 14 and 18. However I am able to plot the vector fields and do everything else. I attached a copy of my work so you can take a look at it and tell me what am I doing wrong. Thank You.