Further, observe that at turning points, the graph has either a little hill or a little
valley Roughly speaking, the function has minimum value in some neighbourhood
(interval) of each of the points A and C which are at the bottom of their respective
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valleys Similarly, the function has maximum value in some neighbourhood of points B
and D which are at the top of their respective hills For this reason, the points A and C
may be regarded as points of local minimum value (or relative minimum value) and
points B and D may be regarded as points of local maximum value (or relative maximum
value) for the function