function plotZeros(f1, f2, xvals, yvals)
% zeigt einen 3d-Plot von f1 und f2 sowie die Schnittlinien
% mit der xy-Ebene
% Parameter:
%   f1, f2: Funktionen zweier Veränderlicher
%   xvals, yvals: x/y-Werte zum Plotten

[X,Y] = meshgrid(xvals, yvals);
Z1 = f1(X, Y);
Z2 = f2(X, Y);

subplot(1,3,1)
view([-20 42]);
hold("on");
surface(X,Y,Z1,"EdgeColor",[.8 .8 .8],"FaceColor","none")
contour(X,Y,Z1,"LevelStep",1000, "LineWidth",2);
colormap("gray")
hold("off");

subplot(1,3,2)
view([-20 42]);
hold("on");
surface(X,Y,Z2,"EdgeColor",[.8 .8 .8],"FaceColor","none")
contour(X,Y,Z2,"LevelStep",1000, "LineWidth",2);
colormap("gray")
hold("off");

subplot(1,3,3)
hold("on");
contour(X,Y,Z1,"LevelStep",1000, "Color", "blue");
contour(X,Y,Z2,"LevelStep",1000, "Color", "red");
hold("off");
set(gcf, "Position", [1 1 900 400]);
