Section 15.2

Plot3D[x^2+y^2,{x,-2,2},{y,-2,2}, RegionFunction->Function[{x,y,z}, -1 <x && x<1 && -1<y&&y<1]]

Plot3D[x^2-y^2,{x,-2,2},{y,-2,2}, RegionFunction->Function[{x,y,z}, -1 <x && x<1 && -1<y&&y<1]]

Plot3D[(x^2)(y^2), {x, -10, 10}, {y, -10, 10}]

Plot3D[(x^3)+(y^3), {x, -10, 10}, {y, -10, 10}]

Section 15.3

Plot3D[3x-2y,{x, -7, 7}, {y, -7, 7},RegionFunction->Function[{x,y,z}, x^2+2y^2<44]]

Plot3D[x+3y,{x, -5, 5}, {y, -5, 5},RegionFunction->Function[{x,y,z}, x^2+y^2<2]]

Plot3D[x+y-(x-y)^2,{x, -.5, 1.5}, {y, -.5, 1.5},RegionFunction->Function[{x,y,z}, 0 <x && 0 <y && x+y <1]]