A function f(x) which is defined as an open interval including the point x = a, is differentiable at that point if which of the following holds true ?
1
\(\lim _{δ x \rightarrow 0}[f(a+δ x)-f(a)] \) ÷ δx exists and is finite
2
\(\lim _{\delta x \rightarrow 0}[f(a+\delta x)-f(a)]\) ÷ x exists and is finite
3
\(\lim _{\delta x \rightarrow 0}[f(a-\delta x)+f(a)]\) ÷ δx exists and is finite
4
\(\lim _{\delta x \rightarrow 0}[f(a-\delta x)-f(a)]\) ÷ x exists and is finite