Question 134680
f(x)=1/x 
f(a+h)=1/(a+h)
f(a)=1/a
f(a+h)-f(a)=((1/(a+h))-(1/a)
...........=(a-(a+h))/(a*(a+h))
...........=-h/(a(a+h)
so [f(a+h)-f(a)]/h=-h/(a(a+h) divided by h
=-1/(a(a+h))