Posted by Laurie on Tuesday, July 7, 2009 at 5:28pm.
Consider the quadratic function
f(x) = – x^2 + 10x – 26. Determine whether there is a maximum or
minimum value and find that value.
Algebra - Marth, Tuesday, July 7, 2009 at 5:34pm
This is algebra?
If you have not learned differentiation, perhaps your teacher wants you to use a calculator to find the extrema. (If you have, disregard this paragraph).
Take the derivative of f(x):
f'(x)= -2x + 10
Set f'(x) = 0
-2x + 10 = 0
10 = 2x
x = 5
Now use a sign line to find whether x=5 is a minimum or maximum.
f'(0) = +
f'(10) = -
x=5 is a maximum because f'(x) changes signs from + to -
Algebra - Reiny, Tuesday, July 7, 2009 at 5:42pm
complete the square,
f(x) = – x^2 + 10x – 26
= - [x^2 - 10x + 25 - 25] - 26
= -(x-5)^2 + 25 - 26
= -(x-5)^2 - 1
so the vertex is (5,-1) and since the parabola opens downwards, it will be a maximum point and the maximum value of the function is -1
Algebra - Laurie, Tuesday, July 7, 2009 at 5:46pm
I do not think these answers are right. I get somethin else and 5 is not an option. Here are the choices
A. Minimum is 25
B. Minimum is -51
C. Maximum is -1
D. Maximum us -51
Algebra - Marth, Tuesday, July 7, 2009 at 5:58pm
5 is the value at which the maximum occurs. f(5) = -1, so choice C.
Algebra - Laurie, Tuesday, July 7, 2009 at 5:59pm
I was thinking that as well! Thanks!
Algebra - Reiny, Tuesday, July 7, 2009 at 6:20pm
that is exactly the answer I gave you, read my last line of my reply please
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