Factoring Rational Functions
Since fractions of polynomials form a field, every element (other than zero)
divides any other, so there is no useful notion of irreducible factors.
Thus the factor operation is not very useful
for fractions of polynomials.
Instead, there is a specific operation
factorFraction that separately
factors the numerator and denominator and returns a fraction of the
factored results.
You can also use map. This expression applies
the factor operation to the numerator and
denominator.
