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Worked example: Evaluating functions from graph

Evaluating a function at x=-1 using the graph of that function. Created by Sal Khan.

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Video 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.