# Simple differentiation question

1. Nov 13, 2014

### Timeforheroes0

Hey guys,
Just a simple question to see if I'm going insane. So say I have an expression for:
$$\frac{dxy}{dt}$$ and an expression for $$\frac{dy}{dt}$$, how to I go about isolating an expression for just $$\frac{dx}{dt}$$
I have tried using the product rule but it doesn't work for what I want. I know this is a very simple question but I haven't done calculus in a long time!

2. Nov 13, 2014

### ShayanJ

$\frac{d(xy)}{dt}=\frac{dx}{dt}y+x\frac{dy}{dt}\Rightarrow \frac{dx}{dt}=\frac{1}{y}(\frac{d(xy)}{dt}-x\frac{dy}{dt})$

3. Nov 13, 2014

### Timeforheroes0

Yeah that's what I did.. I'm doing this in an ode solver in matlab so obviously my code is wrong elsewhere.
thanks!