Find the unknown dimension in the polyhedron: the edge length of a cube w/a diagonal of 9 ft. Please include a formula.

The diagonal of a prism is given by
"

D = sqrt( L^2 + W^2 +
h^2)

But in the cube L
=W+h

==> D = sqrt (
3*L^2)

==> D =
L*sqrt3............(1)

Now we need to find the length of
the side is D= 9

==> 9 =
L*sqrt3

==> L = 9/sqrt3 = 9sqrt3/3 =
3sqrt3.

Then the length of the side of the
cube is 3*sqrt3.