Start with f(x) = (x-9)/(x+5) and g(x) = (-5x-9)/(x-1). To obtain f(g(x)), throw out each appearance of x in f(x) = (x-9)/(x+5) and replace it with g(x) = (-5x-9)/(x-1):
f(g(x)) = [(-5x-9)/(x-1) - 9] / [(-5x-9)/(x-1) + 5]
Now simplify the algebra. If your result equals just x, then you have proven that f and g are inverses of one another. Need help with the fractions? If so, do what you can and share it here; I'd then be glad to give you feedback on your work.
