• Numerator[expr] gives the numerator of expr.
picks out terms which do not have superficially negative exponents. Denominator
picks out the 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 numerators.
• Numerator can be used on rational numbers.
• New in Version 1.