Worked example: Evaluating functions from graph
About this video
Sal finds f(-1) from the graph of a function. He finds x = -1 on the x-axis, looks at where the graph is at that x, and reads off the output: f(-1) = 6.
You'll be able to
- find the value of a function from its graph.
- explain that f(-1) = 6 means the point (-1, 6) is on the graph.
Key words
- graph of a function
- A picture showing the output (height) for each allowed input x.
- f(-1)
- The output of f when the input is -1.
Transcript
The function f of x is graphed. Find f of negative 1. So this graph right over here is essentially a definition of our function. It tells us, given the allowed inputs into our function, what would the function output? So here, they're saying, look, what gets output when we input x is equal to negative 1?
So x equals negative 1 is right over here. x is equal to negative 1. And our function graph is right at 6 when f is equal to negative 1. So we can say that f of negative 1 is equal to 6. Let me write that over here. f of negative 1 is equal to 6.
Video © Khan Academy, used under CC BY-NC-SA. Watch on Khan Academy. Puzzicle is not affiliated with Khan Academy.