With regard to calculus, I never once used the quotient rule after High School because I thought to myself, "Why do I need to memorize another rule when I could just write every single quotient as a product?",(reply>), Multiplicative inverses strike once again,(reply>), same, in fact I multiply both sides by the denominator and use implicit differentiation, that's the easiest way by farrr,(reply>), @鋼の無神論者：The Fullmetal Atheist true,(reply>), Me too. I never use it. Plus I find the expression often nicer when it's not grouped in the same fraction. Leibnitz rule is all you need.