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

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Karl-Olav Nyberg

Posts: 462
Registered: 12/6/04
Re: Help Needed in math
Posted: Apr 30, 2014 5:28 AM
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On Wednesday, April 30, 2014 5:02:27 AM UTC+2, William Elliot wrote:
> 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?


Hi.

Are you asking me why it works? Or is it a retorical question to the OP?
I know why it works :)

KON



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