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# Completing the Square?

Well, i have my math test this week and i don't quite get how you complete the square. Can anyone explain?

Update:

well neither of these explain it well so i'll look it up on google or something.

### 2 Answers

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- 1 decade agoFavorite Answer
If you have a problem of x^2 + 6x + 5 = 0, you would know that in order to get (x + 3)^2, you would need x^2 + 6x + 9 on one side.

So...

x^2 + 6x + 5 = 0

x^2 + 6x + 5 + 4 = 4

(x + 3)^2 = 4

- AntiApollyonLv 61 decade ago
Suppose you have an equation such as:

x^2 + 6x + 5 = 0 and you want to get (x+?)^2

You know that (x+n)^2 = x^2 + 2nx + n^2

Rewrite your equation as

x^2 + 6x = -5

Now, 2n must equal 6, so make n=3

n^2 = 3^2 = 9

Add 9 to both sides:

x^2 + 6x + 9 = -5 + 9

(x+3)^2 = 4

Source(s): calebfurth: How did we both arbitrarily pick the exact same example problem?

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