When we are forced to derive something like:

dy   9x2
dx   3x

We could divide this out or re-write it to allow us to use the product rule, but the simplest way is to use what is called the quotient rule:

(f/g)'(x) = g(x)f'(x)-f(x)g'(x)
All this means is that we {(multiply the denominator with the derivative of the numerator), subtract the product of (the numerator and the derivative of the denominator)} and divide all this mess by the {square of the denominator}.