### 12.12.5 The Cartesian equation of an object in space: equation

See section 11.13.7 for Cartesian equations of
two-dimensional objects.

The equation command takes as argument a geometric object.

equation returns Cartesian equations which specify the
object. The equations will involve z, y and
z, so these variables must be unassigned. If they have
assignments, they can be unassigned with purge(x,y,z).

Input:

equation(line(point(0,1,0),point(1,2,3)))

Output:

x-y+1=0,3*x+3*y-2*z-3=0

Input:

equation(sphere(point(0,1,0),2))

Output:

x^2+y^2+z^2-2*y-3=0