# SparkNotes: Precalculus: Functions

3, what is a function? Domain and range, functional notation: The argument of the function, a function of a function, what is a function? W. HEN ONE thing depends on another, as for example the area of a circle depends on the radius - in the sense that when the radius changes, the area will change - then we say.
When that is the case, we say that y is a function of x. Thus a "function" must be single-valued one and only one. For example, y 2 x 3. To each value of x there is a unique value of y.
Domain and range, the values that x may assume are called the domain of the function. We say that those are the values for which the function is defined. In the function y 2 x 3, the domain may include all real numbers.
X could be any real number. Or, as in Example 1 below, the domain may be arbitrarily restricted. There is one case however in which the domain must be restricted: A denominator may not be 0.
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In this function, x may not take the value 2. For, division by
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