> >
> > http://commons.wikimedia.org/wiki/File:LagrangeMultipliers3D.png
Maybe something like this can help:
load(draw);
/* bell-shaped surface */
f(x, y) := 20*exp(-x^2-y^2)-10;
/* these is how y depends on x in the plane
2*x - y + 1 = 0, parallel to OZ axis */
y(x) := 2*x+1;
draw3d(
/* bell */
color = green,
explicit(f(x,y),x,-2,2,y,-3,3),
contour_levels = 15, /* you can select contours */
contour = both, /* and where to draw them */
/* interseccion curve between bell and plane */
color = blue,
line_width = 3,
parametric(t, y(t), f(t, y(t)), t, -2,1) ) ;
for help, type
? contour
? contour_levels
As Jaime said, you need some hand work to compose the scene.
--
Mario