(commands used to generate figure above)

>	p1:=plot3d(3*x+4*y+6,x=-2..2,y=-x-2..-x+2,color=red,grid=[5,5]): p2:=plot3d(x^2+y^2,x=-2..2,y=-sqrt(4-x^2)..sqrt(4-x^2)): display(p1,p2,view=[-2..2,-2..2,0..7],axes=normal):