pi=N[Pi];
p1=Plot[Sin[x],{x,0,4 pi},AxesLabel->{"x","y"}];
p2=Plot[Cos[x],{x,0,4 pi},PlotStyle->Dashing[{0.01}]];
p3=Show[p1,p2];
bild=Show[p3,Ticks->{{0,Pi,2 Pi,3 Pi,4 Pi},Automatic},
          ImageSize->{400,300}];