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: Finding Ordered pair question

  1. Sep 17, 2010 #1
    1. The problem statement, all variables and given/known data
    Please find all ordered pairs of integers (x,y) such that x2 + 2x + 18 = y2


    2. Relevant equations
    x2 + 2x + 18 = y2


    3. The attempt at a solution

    Im not sure on how to begin. I tried square-rooting the expression, to solve for y, turning it into y = [tex]\sqrt{x + 2x + 18}[/tex]. I would greatly appreciate any help to get me started on this problem.

    Thanks!
     
  2. jcsd
  3. Sep 17, 2010 #2

    Mark44

    Staff: Mentor

    It might be helpful to complete the square. Then you would have the difference of two squares being equal to -17.
     
  4. Sep 18, 2010 #3
    Hey, thanks for the help.
    So after this step, do we use trial and error to find the correct solution. I am getting one ordered pair, (9,9), and (-9,-7) after all the math(since x, and y can only be integers). I would really appreciate it if you could confirm this.
    Thank you
     
  5. Sep 19, 2010 #4

    Mark44

    Staff: Mentor

    Those ordered pairs you got aren't solutions. When you completed the square, what did you get for your equation?
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook