How to complete the square?

This is a handy trick for quadratic equations ax^2 + bx + c = 0.

e.g. (x^2 + 5x + 6). So a = 1, b = 5 and c = 6.

To complete the square, let x^2 + 5x + 6 = 0. Then, take 6 to the other side to get x^2 + 5x = -6.

Now focus on x^2 + 5x. You need to divide 5 by 2 ( = 2.5) and write in the form (x + (b/2))^2 - (b/2)^2 = -6. So you get (x + 2.5)^2 - (2.5)^2 = -6. This equals to (x + 2.5)^2 = 0.25 as (2.5)^2 - 6 = 0.25. Then rearrange for x. (x + 2.5) = +- 0.5. So x = -3 and x = -2.