Skip to main content

Evaluating Functions

Evaluating a function means finding the value of f(x) =… or y =… that corresponds to a given value of x. To do this, simply replace all the x variables with whatever x has been assigned. For example, if we are asked to evaluate f(4), then x has been assigned the value of 4.

Example: Given that f(x) = 3x + 6, find f(2)

Solution: This means we will evaluate the function when x has been assigned the value of 2. The first step is to replace every x with 2. Then evaluate the function by following order of operations (BEDMAS).

f(x) = 3x + 6

So, we have :

f(2) = 3(2) + 6

        = 6 + 6

        = 12

Example: Given the function f(x) = 5x2 - 2√x + 7, evaluate f(-3).

Solution: Substitute -3 in for x and evaluate.

f(-3) = 5(-3)2 - 2√-3 +7

         = 5(9) -2√4

         = 45 – 4

         = 41

Example 1:

Example 2:

University of Ontario Institute of Technology logo