If g(x) is a reflection of f(x) over the x axis, then g(x) = -1*f(x), which can be shortened to g(x) = -f(x). We stick a negative outside the entire f(x) function to flip the signs of each y coordinate. For example, if the point (1,2) was on f(x), then (1,-2) is on g(x).
So f(x) = 5(0.8)^x turns into g(x) = -5(0.8)^x
Answer: Choice B
