Answer: g(x) = -f(x)
Step-by-step explanation:
When we have a point (x, y) and we reflect it over the x-axis, the end result of the reflection is the point (x, -y)
In this case we have a function reflected, and we know that we can write a function as (x, f(x))
So when we reflect it, the result will be (x, g(x)) = (x, -f(x))
So we have g(x) = -f(x)