This is documentation for Mathematica 8, which was
based on an earlier version of the Wolfram Language.
View current documentation (Version 11.1)

Denominator

Denominator[expr]
gives the denominator of expr.
  • Denominator 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.
Extract denominator of a rational number:
Extract denominator of a rational expression:
Extract denominator of a rational number:
In[1]:=
Click for copyable input
Out[1]=
Extract denominator of a rational expression:
In[2]:=
Click for copyable input
Out[2]=
Rational numbers:
Rational expressions:
Select terms with syntactically negative exponents:
All exponents syntactically negative:
No syntactically negative exponents:
Denominator automatically threads over lists:
Find denominators over integers modulo m:
Denominators of trigonometric functions:
Numerator gives the terms without negative exponents:
An expression is a quotient of its numerator and denominator:
Use Cancel to cancel common factors between the numerator and the denominator:
Together writes an expression as a fraction and cancels common terms:
Use ExpandDenominator to directly expand all denominators:
Cyclic addition []:
New in 1