Math 150
Sections 12.1,12.2: Functions of Several Variables

Plot3D[Sin[ x y] / (x y), {x,-10,10}, {y,-10,10}]

Manipulate[Plot3D[Sin[ x y] / (x y), {x,-10 c,10 c}, {y,-10 c,10c}], {c,1,.001}]

Manipulate[Plot3D[{h,Sin[ x y] / (x y)}, {x,-10 c,10 c}, {y,-10 c,10c}], {c,1,.001},{h,-2,2}]

?ContourPlot

Manipulate[ContourPlot[x^2 + a y^2, {x,-4,4},{y,-4,4}], {a,4,-4}]