How do I distinguish between a point of local maxima or minima, when the second derivative in that point is equal to zero?
Got it!snorkack said:"Stationary point" means that first derivative is zero and you specify that second also is.
In that case, if the first nonzero derivative is odd (third, fifth etc.), it is neither maximum nor minimum but a stationary inflection point. If the first nonzero derivative is even (fourth, sixth etc.), the point is minimum if that derivative is positive and maximum if negative.