Question 1064333
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Take (use) a parabola (a quadratic function) as a model, and it will say you everything.


If f''(x) > 0 , it is like a parabola with the leading coef. > 0, i.e. opened upward.


If f''(x) < 0, it is like a parabola with the leading coef. < 0, i.e. opened downward.