# Finding Ordered pair question

1. Sep 17, 2010

### spoc21

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 = $$\sqrt{x + 2x + 18}$$. I would greatly appreciate any help to get me started on this problem.

Thanks!

2. Sep 17, 2010

### Staff: Mentor

It might be helpful to complete the square. Then you would have the difference of two squares being equal to -17.

3. Sep 18, 2010

### spoc21

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

4. Sep 19, 2010

### Staff: Mentor

Those ordered pairs you got aren't solutions. When you completed the square, what did you get for your equation?