with (plots):plot3d([x,y,4-x-2*y], x=-2..2, y=-sqrt(4-x^2)..sqrt(4-x^2),axes=normal);plot3d([u*v,u+v,u-v], u=-1..1, v=-sqrt(1-u^2)..sqrt(1-u^2),axes=normal);plot3d([u*cos(v),u*sin(v),v], u=0..1, v=0..Pi,axes=normal);plot3d([x,y,y+3], x=-1..1, y=-sqrt(1-x^2)..sqrt(1-x^2),axes=normal);