>    restart;

>    f:=(x,y)->4*x^3 + 8*y^4;

f := proc (x, y) options operator, arrow; 4*x^3+8*y^4 end proc

>    g:=(x,y)->12*x+32*y-32;

g := proc (x, y) options operator, arrow; 12*x+32*y-32 end proc

>    plot3d([f,g], -1..2, -1..2, axes=boxed, title="(4.4) Example 1", color=[red,blue]);

[Maple Plot]

>    l:=(x,y)->x+sin(y)+3*x*y^2+exp(x);

l := proc (x, y) options operator, arrow; x+sin(y)+3*x*y^2+exp(x) end proc

>    m:=(x,y)->x+1;

m := proc (x, y) options operator, arrow; x+1 end proc

>    plot3d([l,m], -1..1, -1..1,axes=boxed, lightmodel=none, color=[red,blue],title="(4.4) Example 2");

>   

[Maple Plot]

>   

>   

>    h:=(x,y)->cos(x)^2 * sin(x*y);

h := proc (x, y) options operator, arrow; cos(x)^2*sin(x*y) end proc

>    k:=(x,y)->-x-Pi*y+2*Pi;

k := proc (x, y) options operator, arrow; -x-Pi*y+2*Pi end proc

>    plot3d([h,k], 2..4, 0..2,axes=boxed, lightmodel=none, color=[red,blue],title="(4.4) Example 3");

[Maple Plot]

>