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Math Help - Quadratic Formula Question #3

  1. #1
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    Post Quadratic Formula Question #3

    http://i.imgur.com/kPBi5Ueh.jpg

    #15

    I am not good at creating equations off of word problems... I try but I always get it wrong, I'm not sure how to do any word problems like these.

    275x^2 - 15x - 19600 = 0

    That equation was my attempt at it, not sure if it is correct...

    Any help would be great, thanks!
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  2. #2
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    Re: Quadratic Formula Question #3

    if R is the revenue, S is the number of sales and P is the price. R=SP
    When the price is decreased by $15 x times the price is 275-15x and the sales is 90+5x.
    You want to find x when R>19600
    Thanks from Mathnood768 and topsquark
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  3. #3
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    Re: Quadratic Formula Question #3

    Shakarri has given the correct direction. Form the equation for R
    you will get R = x^2+104x-206
    Now proceed to differentiate to get min value of x.
    Thanks from Mathnood768
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  4. #4
    MHF Contributor MarkFL's Avatar
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    Re: Quadratic Formula Question #3

    Since this question is posted in the Pre-Calculus forum, you may not know how to use differential calculus to optimize a function. In this case, since you have a quadratic, look for the axis of symmetry.
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