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# max value of quadratic expression watch

1. What does it mean to find the maximum value of an expression, i.e A = 20x - 2x^2 (find maximum value of A)

How should I do it?
2. (Original post by 0j0)
What does it mean to find the maximum value of an expression, i.e A = 20x - 2x^2 (find maximum value of A)

How should I do it?
Try sketching a graph of the quadratic (with A on the y-axis). Then think about how you can find the maximum value of A.
3. oh i see, of course! thanks
4. To find the max value of a quadratic expression, complete the square of it.
E.g.
A = 20x-2x^2=0
2x^2-20x=0
a=2,b=-20,c=0
2((x-5)^2)-(5^2)=0
2(x-5)^2-25=0

The next step is to get the max value of x by inversing the constant term what is in the bracket and finding the inverse of it, this results in extracting the -5 2(x-5)^2 and inversing it to +5. Therefore max(x) = 5

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Updated: October 5, 2017
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