Based on the graph, the input value for which f(x) = 3 is -3.
What is a function?
In Euclidean Geometry, a function is a mathematical expression which is used for defining and representing the relationship that exists between two or more variables such as an ordered pair.
This ultimately implies that, a function is typically used in mathematics for uniquely mapping an input variable to an output variable.
By critically observing the graph shown above, we can logically deduce that an input value that produces an output value of 3 is -3 as made evident by this ordered pair (3, -3);
f(-3) = 3