A real function \(f\) defined on an interval \([a,b]\) with \(a<c<b\) where \(c\) is a point of the interval, is said to be differentiable at the point \(x=c\) if
\(\(f'(c)=lim_{x}\frac{f(x)-f(b)}{x-c}\) exist and is infinite
—>> \(\(f'(c)=lim_{x\rightarrow c}\frac{f(x)-f(c)}{x-c}\) exist and is finite
\(\(f'(c)=lim_{x\rightarrow c}\frac{f(c)-f(b)}{a-b}\) exist
\(\(f'(c)=lim_{x\rightarrow c}\frac{f(a)-f(c)}{b-c}\) exist and is finite
