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Find the maximum or minimum value of the function.

f(x) = 9 − x −   1/2x^2
 Jun 25, 2014

Best Answer 

 #1
avatar+129852 
+10

f(x) = 9 − x −   1/2x^2   

Rewrite as

f(x) = -(1/2)x^2 - x + 9

This is a parabola that opens downward . so it will have only a maximum. If you haven't had calculus, the x coordinate of the max is given by -b/2a, where b = -1 and a = -1/2 ....So we have...

x = -(-1)/2(-1/2)  = 1/-1 = -1

Now, to find the y coordinate, we just substitute for x in the function.  So we have...

(-1/2)(-1)^2 - (-1) + 9 =   (-1/2) + 1 + 9 =  9.5

So the max occurs at (-1, 9.5)   ....  Here's the graph

 Jun 25, 2014
 #1
avatar+129852 
+10
Best Answer

f(x) = 9 − x −   1/2x^2   

Rewrite as

f(x) = -(1/2)x^2 - x + 9

This is a parabola that opens downward . so it will have only a maximum. If you haven't had calculus, the x coordinate of the max is given by -b/2a, where b = -1 and a = -1/2 ....So we have...

x = -(-1)/2(-1/2)  = 1/-1 = -1

Now, to find the y coordinate, we just substitute for x in the function.  So we have...

(-1/2)(-1)^2 - (-1) + 9 =   (-1/2) + 1 + 9 =  9.5

So the max occurs at (-1, 9.5)   ....  Here's the graph

CPhill Jun 25, 2014

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