**2.1: Introduction to Functions - Mathematics LibreTexts**
https://math.libretexts.org/Bookshelves/Algebra/Intermediate_Algebra_(Arnold)/02%3A_Functions/2.01%3A_Introduction_to_Functions

WebThe idea of mapping gives us an alternative way to describe a function. We could say that a function is a rule that assigns a unique object in its range to each object in its domain. Take for example, the function that maps each real number to its square. If we name the function f, then f maps 5 to 25, 6 to 36, −7 to 49, and so on.

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