Hello,
considering the definition of derivative, what would the following quantity be equal to?
[tex]\lim_{\delta \to 0} \frac{f(x+g(\delta))f(x)}{g(\delta)}[/tex]
In this case [itex]g(\delta)[/itex] is a monotonic increasing function such that g(0)=0.
For example we might have [itex]g(\delta)=\delta^3[/itex]
