• Denominator[expr] gives the denominator of expr.
picks out terms which have superficially negative exponents. Numerator
picks out all remaining terms.
• An exponent is "superficially negative" if it has a negative number as a factor.
• The standard representation of rational expressions as products of powers means that you cannot simply use Part
to extract denominators.
• Denominator can be used on rational numbers.
• New in Version 1.