Calculus functions help.

f(x) = 8 / (x)^2
find and simplify: ( f(x + h) - f(x) ) / h )

Plug in (x+h) for x.
([8/ (x+h)^2] - [8/ x^2]) * (1/h)

Find the common denominator by cross multiplying.

[(8x^2) - 8(x+h)^2] / [((x+h)^2)(x^2)] *(1/h)

Distribute and Simplify.
[(8x^2) - 8(x^2 + 2xh + h^2)] / [(x^2 + 2xh + h^2)(x^2)] *(1/h)
[(8x^2) - 8x^2 - 16xh - 8h^2)] / [((x^2 + 2xh + h^2)(x^2)] *(1/h)
(-16xh - 8h^2) / ((x+h)^2)(x^2)(h)

Take out the h from the nominator. It crosses out with the h in the denominator.
Now, you are left with:
(-16x - 8h) / ((x+h)^2)(x^2)

I am assuming lim h->0, right?
so plug in 0 wherever there's a h and you'll get the derivative (the answer).

Hope this helps :)

you're pretty much finding the derivative which is what you will learn shortly; the answer will be -16x^-3


so just fill in the equation into the other equation to get -16x^-3