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Math Help - Quadratic formula

  1. #1
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    Exclamation Quadratic formula

    I need help getting the variable b by itself

    this is what i have so far but need help finishing it. If you could show step by step instructions that'd be great.
    (2a)(2a)
    2ax=-b +/- sqrt(b^2-4ac)
    +b +b
    (2ax+b)^2= +/-sqrt( b^2-4ac)^2
    (2ax+b)^2= b^2-4ac
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  2. #2
    MHF Contributor MarkFL's Avatar
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    Re: Quadratic formula

    If you are trying to take the quadratic formula and solve for b, it will be far simpler to take the quadratic from which the formula is derived, and solve that for b:

    ax^2+bx+c=0

    bx=-(ax^2+c)

    b=-\frac{ax^2+c}{x}
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  3. #3
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    Re: Quadratic formula

    I know t would be easier to do it that way but the question asks to go from the formula i posted but thanks!
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  4. #4
    MHF Contributor MarkFL's Avatar
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    Re: Quadratic formula

    Well, we can begin with the quadratic formula:

    x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}

    2ax=-b\pm\sqrt{b^2-4ac}

    2ax+b=\pm\sqrt{b^2-4ac}

    4a^2x^2+4abx+b^2=b^2-4ac

    4a^2x^2+4abx+4ac=0

    With a\ne0 we have:

    ax^2+bx+c=0

    Now, follow my first post.
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