Final form, nothing changed, I just added an example.

This project has 4 parts. All plots need your name as part of the title.
Each part has 2 plots, a 3d plot with the axis labeled and a combined
density and contour plot. All plots are over the range 0 - 2pi by 0 - 2pi.

Part 1. sin(x+y)

Part 2. sin(xy)

Part 3. sin(x)+sin(y)

Part 4. sin(x)sin(y)

The following example will help maple users
f:=(x,y)->x^2+y^2;
L:={seq(f(x,y)=2*i,i=1..9)};
a:=implicitplot(L,x=-3..3,y=-3..3):
b:=densityplot(x^2+y^2,x=-3..3,y=-3..3):
display({a,b});

For once, mathematica users win, this is the default behavior for ContourPlot.
ContourPlot[x^2+y^2,{x,-3,3},{y,-3,3}]

From proj3.txt
maple: To combine two 2D plots try:

a:=gradplot(x^2+y^2,x=-5..5,y=-5..5):
                                    ^ note the : and not ; try it both ways.
b:=implicitplot(x^2+y^2=16,x=-5..5,y=-5..5):
display({a,b}); <- back to semi-colon.

mathematica: To combine two 2D plots try:

<<"Graphics/PlotField.m"
a=PlotGradientField[x^2+y^2,{x,-5,5},{y,-5,5}];
b=Plot[x,{x,-5,5}];
Show[a,b]