# Problem with Lagrangian function

1. Sep 4, 2015

### Mateusz

Hello,
I trying to understood some transition from one equation to another but i need a little help with that.
So we have, a

Last edited: Sep 4, 2015
2. Sep 4, 2015

### Geofleur

Use a Taylor expansion, $f(x+\Delta x) \approx f(x) + \frac{df}{dx}\Delta x$ with $f = L$, $x = v^2$, and $\Delta x = 2v\epsilon$.

3. Sep 5, 2015

### Mateusz

Ohh so when he said "powers series" he means "Taylor expansion", thank you :)