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Math Help - How to do quadratic formula?

  1. #1
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    How to do quadratic formula?

    I have an equation 2x^2+x-1

    How do I rewrite in parenthesis? Like (x+ )(x- )
    Etc.


    I got x = .5 and -1 using quadratic formula
    Thanks
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  2. #2
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    Re: How to do quadratic formula?

    Just a heads up, this isn't a calculus problem.

    Anyways, I believe you can only factor a quadratic ax^2 +bx+c strictly into the form (x + h)(x+k) when a=1

    You can still factor by grouping though.
    Last edited by ReneG; June 25th 2013 at 08:57 PM.
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  3. #3
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    Re: How to do quadratic formula?

    Quote Originally Posted by minneola24 View Post
    I have an equation 2x^2+x-1

    How do I rewrite in parenthesis? Like (x+ )(x- )
    Etc.


    I got x = .5 and -1 using quadratic formula
    Thanks
    To start with, you need to find two numbers that multiply to give "ac" and add to give "b".
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  4. #4
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    Re: How to do quadratic formula?

    In general for a quadratic equation ax^2 + bx + c = 0 for factorization just write the product of the coefficient of x^2 and constant, in this case ac. Thereafter find such factors of the product ac such that their sum is equal to the coefficient of x. there after split the middle term and group into factors.
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  5. #5
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    Re: How to do quadratic formula?

    The reason I put it in calculus is because im doing a partial fraction integral and need to seperate the denomenamtor.

    I'm still confused how to use the quadratic formula to factor into (x )(x )

    Because I get .5 and -1 from the quadratic formula

    However graphing (x-.5)(x+1) does not give the same as the original equation :S
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  6. #6
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    Re: How to do quadratic formula?

    Quote Originally Posted by minneola24 View Post
    I have an equation 2x^2+x-1
    How do I rewrite in parenthesis? Like (x+ )(x- )
    Etc.
    I got x = .5 and -1 using quadratic formula
    .

    It is simple: ax^2+bx+c can always be factored,
    \left( {x - \frac{{ - b + \sqrt {{b^2} - 4ac} }}{{2a}}} \right)\left( {x - \frac{{ - b - \sqrt {{b^2} - 4ac} }}{{2a}}} \right).
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  7. #7
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    Re: How to do quadratic formula?

    Perhaps it is that "2" that is bothering you knowing that .5 and -1 are roots of the polynomial tells you that you want (x- .5)(x- (-1))= (x- .5)(x+ 1) However, with that "2" coefficient of x^2 you need 2(x- .5)(x+ 1).
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  8. #8
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    Re: How to do quadratic formula?

    Thanks. So if it was 4x^2 as a coefficient I would do the quadratic formula and times it by. 4 in the parenthesis version?
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  9. #9
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    Re: How to do quadratic formula?

    Quote Originally Posted by ibdutt View Post
    In general for a quadratic equation ax^2 + bx + c = 0 for factorization just write the product of the coefficient of x^2 and constant, in this case ac. Thereafter find such factors of the product ac such that their sum is equal to the coefficient of x. there after split the middle term and group into factors.
    in this case your equation is 2x^2 + x - 1
    step 1: Product of coefficient of x square 9 in this case = 2 0 and constant term 9 in this case = -1 ) is = -2
    step 2. factors of -2 are
    -2 = 1x -2 = -1 x 2
    step 3. select the factors whose sum is equal to the coefficient of x. in this case 2 + ( -1 ) = 1
    step 4. split the middle term with these factors.
    2x^2 + 2x - x - 1 = 2x ( x + 1 ) -1 ( x + 1 ) = ( x+1 ) ( 2x - 1)
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