Originally Posted by

**dokrbb** thanks a lot for this detailed solution,

although, the program we are entering our answers "asked" me imperatively to do a step further and factor x^2 under the radical; it considered this answer as not correct until I did the following:

$\displaystyle \frac{dy}{dx} &= \frac{5}{x^2\,\sqrt{ 36 - (1/x^2) }}$

IMO it's kind of useless... maybe there is a reason(I'm serious, actually - it's not sarcasm), from a deep mathematical point of view and me, as a novice, I am not aware of... what do you think?