SOLUTION: Find the vertex of f(x)-x^2-10x+21. Is the vertex the maximum or minimum of f? How do you know?

Question 202138: Find the vertex of f(x)-x^2-10x+21. Is the vertex the maximum or minimum of f? How do you know?
Answer by vleith(2983) (Show Source): You can put this solution on YOUR website!
Is the vertex the maximum or minimum of f? Yes it is either the min or the max, depending on which way the function 'opens'
How do you know? Look at the sign of the x^2 term. If it is positive, then the function opens upward --> the vertex is a minimum. If the sign is negative, the the function opens downward --> the vertex is a maximum.
here is a URL where you can plot this --> http://www46.wolframalpha.com/
I am not sure if you meant to write
or that sign makes all the difference
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