> with(DEtools);

>

> ode1:=diff(Q(t),t)=1/10-Q(t)/500;

Den generelle løsning er

> dsolve(ode1,Q(t));

Den partikulære løaning med Q(0)=800:

> dsolve({ode1,Q(0)=800},Q(t));

Den partikulære løsning har grafen

> plot([50+750*exp(-t/500),200],t=0..1400,thickness=2,color=[blue,yellow],title="PCB i akvariet (eks 8)",style=[line,point]);

> solve(50+750*exp(-t/500)=200,t);

> evalf(%);

Eks 9

> ode2:=diff(Q(t),t)=1/10-Q(t)/(1000+t);

> dsolve(ode2,Q(t));

> dsolve({ode2,Q(0)=800},Q(t));

> phaseportrait(ode2,Q(t),t=0..5000,[[Q(0)=800]],Q=200..800,arrows=none,thickness=2,linecolor=[blue],title="PCB i akvariet (eks 9)");

>