An unknown is an independent variable of a function. A function with independent variables is said to be a function "in," "with," or "of" unknowns.
Unknown
See also
Indeterminate, VariableThis entry contributed by Breckin Loggins
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Cite this as:
Loggins, Breckin. "Unknown." From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/Unknown.html