How do I differentiate $f(x) = 7 + 6/x + 6/x^2$? the problem is the following:
with the definition of the derivative, calculate 
f(x) = $7+\frac 6x+ \frac6{x^2}$
I tried to solve it a bunch of times but I just don't get the correct answer
**edit: I must solve it with the def of the derivative

$$f’(x) = \frac{-6}{x^2} + \frac{-12}{x^3}$$
Here we are basically using the formula :
$$(\frac{u}{v} )’ = \frac{u’v-v’u}{v^2}$$
