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Topic: Help Needed in math
Replies: 25   Last Post: May 2, 2014 6:01 PM

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William Elliot

Posts: 2,637
Registered: 1/8/12
Re: Help Needed in math
Posted: Apr 29, 2014 11:02 PM
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On Tue, 29 Apr 2014, konyberg wrote:
> > Find the largest values of the integer a for which ax^2-5x-3 is negative for all values of x.
> set a = (5x + 3) / x^2 and find the minima of this function. This will, with
> your constraints, give the answer: a = -3

5/x + 3/x^2
-5/x^2 - 6/x^3 = 0
-5x + -6 = 0
x = -6/5
a = (-6 + 3)/(36/25) = -25/12
Why does the minimum work?

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