need improvement with axis labels and heavy axis lines
poor eyes here, thanks
not like fortran, how to extend lines?
t = var('t') y = function('y')(t) ye = desolve(diff(y,t) == 210^(-5)y(1500-y), y, ics=[0,50]) ye = ye3/100 yt = solve(ye.simplify_log(), y) show(expand(yt)) P = plot((1500e^(3/100t)/(e^(3/100*t) + 29)),t,0,250, color='red', thickness = 10 ) L = line([(0,1500), (260,1500)], linestyle=":", color="grey", thickness = 10) show(P+L, figsize=5)