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# Evaluate a function: graph

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

Video transcript

PROBLEM: "The function f(x) is graphed. Find f(-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 = -1?” So x = -1 is right over here. x = -1. And our function graph is right at 6 when f is equal to -1. So we can say that f(-1) = 6. Let me write that right over here. f(-1) = 6.