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.Question
Evaluate the function f(x) = 2x + 1 at x = 2.Step-by-Step:
1
Write the function.
f(x) = 2x + 1
Note: 2x = 2 × x.
2
Substitute x = 2 into the function.
f(2) = 2 × 2 + 1
f(2) = 4 + 1
f(2) = 5
Answer:
If we evaluate f(x) = 2x + 1 at x = 2, we get 5. f(2) = 5.A Note on Notation
If a function f is evaluated at a number (e.g. 2), this is denoted f(2).
This page was written by Stephen Clarke.
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