## What you’ll learn to do: Analyze and graph rational functions

Suppose we know that the cost of making a product is dependent on the number of items, $x$, produced. This is given by the equation $C\left(x\right)=15,000x - 0.1{x}^{2}+1000$. If we want to know the average cost for producing $x$ items, we would divide the cost function by the number of items, $x$.

The average cost function, which yields the average cost per item for $x$ items produced, is

$f\left(x\right)=\dfrac{15,000x - 0.1{x}^{2}+1000}{x}$

Many other application problems require finding an average value in a similar way, giving us variables in the denominator. Written without a variable in the denominator, this function will contain a negative integer power.

In the last few sections, we have worked with polynomial functions, which are functions with non-negative integers for exponents. In this section, we explore rational functions, which have variables in the denominator.

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