how would you solve this: if g(a)= (a-1)/a+1), and you have to find (g(a+h)-g(a))/h.

I think you had this set up OK on the other forum, so I will continue from there.

\frac{a+h-1}{a+h+1}-\frac{a-1}{a+1}

Now, your LCD is (a+1)(a+h+1)

So, subtract like any other fraction.

\frac{(a+1)}{(a+1)}* \frac{(a+h-1)}{(a+h+1)}-\frac{(a-1)}{(a+1)}*\frac{(a+h+1)}{(a+h+1)}

Now, continue.