1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Ax^2-40x+40=0 homework problem help

  1. Jul 12, 2004 #1


    User Avatar

    if you can solve ax^2-40x+40=0 for a and x that would be great
  2. jcsd
  3. Jul 12, 2004 #2


    User Avatar
    Science Advisor
    Homework Helper

    No. We have two unknowns (a and x) and one equation. At best, we can express a in terms of x, and vice versa, but no better. To express x in terms of a, simply apply the quadratic formula to the equation you have. You'll get:

    [tex]x = \frac{20 \pm 2\sqrt{10(10 - a)}}{a}[/tex]
  4. Jul 12, 2004 #3
    use this formula [tex]\frac{-b ^+_- \sqrt{b^2 - 4ac}}{2a}[/tex]where a=a, b=-40 and c=40

    Paden Roder
  5. Jul 12, 2004 #4
    Well, sorry! I just stated the quadratic formula, as AKG said. This was the first time I have used LaTeX though, pretty cool, once you get the hang of it.

    Paden Roder
  6. Jul 12, 2004 #5


    User Avatar

    i still don't get it can some one give me a walk through on how to use them with this problem/
  7. Jul 12, 2004 #6


    User Avatar

    a= 0 x= 1
    i just fount it
  8. Jul 12, 2004 #7

    I bet there are millions of answers for this one.

    I came up with a = 10, x = 2
  9. Jul 12, 2004 #8

    I bet there's more than that. In fact, I bet the set of all possible answers is uncountably infinite. I'd bet a lot of money on it, since, as AKG said, with one equation and two unknowns, this isn't going to go anywhere.
  10. Jul 12, 2004 #9


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    Now, while the others have shown how to find x given a, here's how you may find the a-value for any choice of x-value:
    Rewrite this as:

    Hence, for any non-zero choice of x, only a single value for a is allowed by the equation.
  11. Jul 24, 2004 #10
    Is this the whole question?
    Unless it's an 'express x in terms of a' type question you can't solve it with only that information.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook