Answer:
Find the places where the derivative is zero and the second derivative is positive.
Explanation:
By definition, a function has a minimum where the first derivative is zero and the second derivative is positive.
That will be a "local" minimum if there are other points on the function graph that have values less than that. It will be a "global" minimum if there are no other function values less than that. A global minimum is also a local minimum.
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On a graph, a local minimum is the bottom of the "U" where the graph changes from negative slope to positive slope.