# If f(x) = 4x + 5, what is f(-1)?

## Question:

If f(x) = 4x + 5, what is f(-1)?

## Evaluating a Function

When we evaluate a function, we substitute a number in for the variable. We then apply the order of operations to find the overall value of the expression that results from that substitution.

We have a function given in this problem. If we want, we can evaluate this function at a specific value for x. The notation given, f(-1), tells us that we want to know the value of this function when x is set to equal -1. Let's substitute -1 in for the variable and calculate the result.

{eq}\begin{align*} f(-1) &= 4(-1)+5\\ &= -4+5\\ &= 1 \end{align*} {/eq}