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Math Help - Help me with Completing the square

  1. #1
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    Help me with Completing the square

    2x^2 = 3x - 7

    I understand up to a certain point ;

    1. 2x^2 = 3x - 7 ( subtracting 3x )

    2. 1/2(2x^2 - 3x ) = 1/2(-7) ( multiplying by 1/2 to make the x^2 - coefficent 1)

    3. x^2 - 3/2x = -7/2 ( miltiplying and simplifying )


    according to the text it says

    x^2 - 3/2x + 9/16 = -7/2 + 9/16 i don't understand how they
    got that result
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  2. #2
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    You could use the general formula, then it is just a matter of plugging in a,b, and c.

    In this case, a=2, b=-3, c=7

    a(x-\frac{b}{2a})^{2}+\underbrace{c-\frac{b^{2}}{4a}}_{\text{constant}}
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  3. #3
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    more confused

    that formula got me more confused. Can you elaborate on that formula like where you got that from
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  4. #4
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    Look at your step 3, to complete the square you need b^2 as missing third item in general formula: (a+b)^2= a^2+2ab+b^2. Your a^2 is x^2, 2ab is 3/2x, which gives you b: 2ab= 3/2x=2* x* 3/4, 3/4 is b, then b^2 is 9/16. If it's missing, add it to both sides and your left side is completed!
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