x, y = var('x,y')
plot3d(x^2 + y^2, (x,-2,2), (y,-2,2))

x, y = var('x,y')
plot3d(x^2 + y^2, (x,-6,6), (y,-6,6))

x, y = var('x,y')
plot3d(x^4 + y^4, (x,-2,2), (y,-2,2))

x, y = var('x,y')
plot3d(x^3 + y^3, (x,-2,2), (y,-2,2))

u, v = var('u, v')
f_x(u, v) = u
f_y(u, v) = v
f_z(u, v) = u^2 + v^2
parametric_plot3d([f_x, f_y, f_z], (u, -2, 2), (v, -2, 2))

x, y, z = var('x, y, z')
implicit_plot3d(x^2 + y^2 + z^2 - 4, (x,-2, 2), (y,-2, 2), (z,-2, 2))

u, v = var('u,v')
fx = u*v
fy = u
fz = v^2
parametric_plot3d([fx, fy, fz], (u, -1, 1), (v, -1, 1),
                  frame=False, color="red")

u, v = var('u,v')
fx = (1+cos(v))*cos(u)
fy = (1+cos(v))*sin(u)
fz = -tanh((2/3)*(u-pi))*sin(v)
parametric_plot3d([fx, fy, fz], (u, 0, 2*pi), (v, 0, 2*pi),
                  frame=False, color="green")

u, v = var('u,v')
fx = (3+sin(v)+cos(u))*cos(2*v)
fy = (3+sin(v)+cos(u))*sin(2*v)
fz = sin(u)+2*cos(v)
parametric_plot3d([fx, fy, fz], (u, 0, 2*pi), (v, 0, 2*pi),
                  frame=False, color="black")

x, y, z = var('x,y,z')
f(x, y, z) = 4*x^2 * (x^2 + y^2 + z^2 + z) + y^2 * (y^2 + z^2 - 1)
implicit_plot3d(f, (x, -0.5, 0.5), (y, -2, 2), (z, -1, 1))