   # Evaluating Functions

 Our Algebra 1 tutorial software program contains over 60 topic areas. One of them is Evaluating Functions, and this page summarizes the main ideas of this topic. This page is intended for review, and is not a substitute for the interactive, self-paced tutorials of the MathTutor algebra 1 software program.

General Explanation

The concept of FUNCTION is an important one in algebra. In the equation y=x2, the value of y is determined by the value of x, so we say that y is a function of x. For any given value of x, we can find y by simply plugging x's value into the right hand side of the equation wherever x appears. When y is a function of x, we often show "f(x)" on the left side of the equation in place of y.

Let's consider the following function:
```f(x) = 9x2 + 8x - 5
```
What is f(x) at x=4?

To evaluate this function, we simply replace every x with 4:
```f(4) = 9 * (4)2 + 8 * (4) - 5 = 171
```

Sample Problem

In the function below, what is f(x) at x = -7?
```f(x) = 6x2 - 5x + 1
```

Solution

First replace every instance of x with -7:
```f(x) = 6 * (-7)2 - 5(-7) + 1
```
Now simplify and solve:
```f(x) = 6 * 49 + 35 + 1 = 294 + 35 + 1 = 330
```