Needs["Calculus`FourierTransform`"]; f=If[x>-0.25 && x<0.25,1,0]; reihe=NFourierTrigSeries[f,x,10,AccuracyGoal->4] bild=Plot[{f,reihe},{x,-0.5,0.5}, PlotStyle->{Dashing[{0.01}],{}},AxesLabel->{"x","y"}, ImageSize->{400,300}];