What is "when f(x)=4?

When the function f(x) is equal to 4, it means that for any value of x, the output or y-value of the function will always be 4. In other words, f(x) outputs a constant value of 4 regardless of the input x.

This type of function is called a constant function because the output remains the same for all values of x. The graph of f(x) = 4 is a horizontal line passing through the point (0,4) on the y-axis.

A constant function like f(x) = 4 is useful in many mathematical and practical applications where a fixed value or constant is needed.