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Math Help - Stuck

  1. #1
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    Stuck

    The instructions say just to solve.
    x^2 +2x -4
    x^2 + 2x = 4
    Now I add (b/2a)squared which would be (4/4)which equals 1
    x^2 + 2x +1 = 4 + 1
    x^2 +2x + 1= 5
    stuck as to what to do next?
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  2. #2
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    Hi

    x + 2x + 1 = (x+1)
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  3. #3
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    sorry I don't think you understood because I wrote in wrong
    x^2 +2x - 4 = 0
    x^2 +2x = 4
    then I add 1/2 of the coefficient of x and square it, then add the results to both sides of the equation. Therefore I have (2/2)squared which gives me (4/4) which is 1
    x^2 + 2x + 1 = 4 + 1
    x^2 + 2x + 1 = 5
    x^2 + 2x + 1 - 5 = 5-5
    x^2 + 2x - 4 = 0
    Now I am stuck if I have done everything else right
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  4. #4
    Super Member Matt Westwood's Avatar
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    You did all the hard work to get:
    x^2 + 2x + 1 = 5

    and then undid it all by subtracting 5 from it again.

    take a look at the last answer you got:
    x^2 + 2x + 1 = (x+1)^2

    That's why this technique is called "completing the square".
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  5. #5
    MHF Contributor

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    Quote Originally Posted by Brama Bull View Post
    sorry I don't think you understood because I wrote in wrong
    x^2 +2x - 4 = 0
    x^2 +2x = 4
    then I add 1/2 of the coefficient of x and square it, then add the results to both sides of the equation. Therefore I have (2/2)squared which gives me (4/4) which is 1
    x^2 + 2x + 1 = 4 + 1
    x^2 + 2x + 1 = 5
    This is where you stopped before and this is where you should have stopped! Do you understand why "add 1/2 of the coefficient of x and square it"? The whole purpose is to make one side a "perfect square". That was why running gag said " x^2+ 2x+ 1= (x+1)^2".

    Can you solve (x+1)^2= 5?

    x^2 + 2x + 1 - 5 = 5-5
    x^2 + 2x - 4 = 0
    Now I am stuck if I have done everything else right
    These last two lines just undo what you did in the first two lines!
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