How to Evaluate a Function
Evaluating a Function
A function is a relation between a set of inputs and a set of outputs, such that each input is related to exactly one output.
Evaluating a function means putting an input into a function, and finding the output it relates to.
Understanding Evaluating a Function
To evaluate a function means to see what output an input is mapped to.
The image below shows a mapping diagram which relates a set of inputs to a set of outputs.
If we wanted to evaluate the function when the input is 2, we would see which output it is mapped to.
Imagine we have the function below:
If we evaluate the function at x = 2, we need to find f(2).
A Real Example of How to Evaluate a Function
Evaluating a function is easy.
Evaluate the function f(x) = 2x + 1 at x = 2.
Write the function.
f(x) = 2x + 1
Note: 2x = 2 × x.
Substitute x = 2 into the function.
f(2) = 2 × 2 + 1
f(2) = 4 + 1
f(2) = 5
If we evaluate f(x) = 2x + 1 at x = 2, we get 5.
f(2) = 5.
The slider below another example of how to evaluate functions.Open the slider in a new tab