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Mathematica Teacher's Edition

Built-in Functions

Mathematical Functions

Numerical Functions

Sign

Sign[x] gives -1, 0 or 1 depending on whether x is negative, zero, or positive.

For non-zero complex numbers z, Sign[z] is defined as z/Abs[z].
Sign tries simple transformations in trying to determine the sign of symbolic expressions.
For exact numeric quantities, Sign internally uses numerical approximations to establish its result.
See The Mathematica Book on the web: Section 3.2.2.
See also: Abs, Positive, Negative, NonNegative, Greater, Simplify.

Further Examples