oh.. the clue is to use the second sentence of Weirestress..
is a continous function at which gets a local maximum at point . i need to prove - formal proof, not just words - that if doens't have any other extremas, gets maximum at
for clarification of how us in the course define extrema: " is an extrema value if is a local minimum or a local maximum of . in this case we'd say that the point on 's graph is called an extrema of "