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 ago
    Favorite 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

  • 1 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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