Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Notice: We are no longer accepting new posts, but the forums will continue to be readable.

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

 Messages: [ Previous | Next ]
 William Elliot Posts: 2,637 Registered: 1/8/12
Re: Help Needed in math
Posted: Apr 30, 2014 11:59 PM

> > > > > > 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?

> a < f(x) = (5x + 3) / x^2, x <> 0
What's f?
> If a < f(x) for all x, then a has to be less than the global minimum of f(x).
> The global minimum of f(x) = -25/12. The largest integer less than this is -3.

Date Subject Author
4/28/14 punisher
4/28/14 quasi
4/29/14 Peter Percival
4/29/14 Karl-Olav Nyberg
4/28/14 Peter Percival
4/29/14 William Elliot
4/29/14 Peter Percival
4/29/14 Karl-Olav Nyberg
4/29/14 Karl-Olav Nyberg
4/29/14 Karl-Olav Nyberg
4/29/14 Karl-Olav Nyberg
4/29/14 William Elliot
4/30/14 Karl-Olav Nyberg
4/30/14 William Elliot
4/30/14 Karl-Olav Nyberg
4/30/14 William Elliot
5/1/14 Karl-Olav Nyberg
5/1/14 William Elliot
5/1/14 quasi
5/2/14 William Elliot
5/2/14 quasi
5/2/14 William Elliot
5/2/14 snmpprotocol@gmail.com
5/2/14 quasi
5/2/14 Karl-Olav Nyberg
5/2/14 quasi