You could try something like this,
with(plots): sol := Optimization:-Maximize( x+y, {2*x+y<=4, x>=0, y>=0} ); optpt := [eval(x,sol[2]), eval(y,sol[2]), sol[1]]; # optimal [x,y,z] common := style=patchnogrid, transparency=0.4: xrng,yrng,zrng := x=0..10, y=0..10, z=-10..10: display( pointplot3d( [optpt], symbol=solidsphere, symbolsize=30, color=red ), plot3d( x+y, xrng, yrng, style=patch ), implicitplot3d( x=0, xrng, yrng, zrng, common ), implicitplot3d( 2*x+y-4, xrng, yrng, zrng, common ), axes=box, view=[0..4,0..5,0..10] );
Another way is to invoke the Optimization:-Interactive() command, which brings up a pop-up assistant. In that assistant, enter the constraints and objective, toggle it as maximize
, hit the Solve button, then the Plot button, and then change the returned object to be the Plot, and then Quit it. That should produce a similar 3D plot.
This question probably belongs more on www.stackoverflow.com (with the Maple tag) than here, as it's more a Maple programming question than a math question. You can also ask questions on www.mapleprimes.com