Cube of Volume a and circumscribed cube.
As you see, the computation of the cube root of a is equivalent
to determining the solution of f (x) = −x3+3kx2 −3k2x+k3 −a =
0. However, if the inscribed and circumscribed cubes are chosen
such that the lengths of their sides are very close to the length of
the side of the cube having volume a, then the value of |x| is very small.