pic1:=plot3d([x, y,(x *y)],x=-4

pic1:=plot3d([x, y,(x *y)],x=-4..4,y=-4..4,axes=boxed,color=brown):
pic2:=plot3d([x,y,2*x-y+2],x=-4..4,y=-4..4,axes=boxed,color=cyan):
display({pic1,pic2});