rational and rationalize convert
reals
to rationals.
If number is already rational, it is returned.
If number is a float,
rational returns a rational
that is mathematically equal in value to the float.
rationalize returns a rational that
approximates the float to the accuracy of
the underlying floating-point representation.
rational assumes that the float is completely accurate.
rationalize assumes that the
float is accurate only to the precision of the
floating-point representation.