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Math Help - quadratic equation word problem

  1. #1
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    quadratic equation word problem

    1. two numbers differ by 17. find the numbers that produce a minimum product.
    (i tried it out and my answer is -8.5 and 8.5, however i dont think that is right)

    2. the sum of base & height of a triangle is 21cm. determine the max area of the triangle in sq centimetres.
    (i managed to get A = 21x - x^2/2, but i dont know how to approach it from there)

    thanks :]
    Last edited by checkmarks; February 17th 2007 at 01:57 PM.
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  2. #2
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    Quote Originally Posted by checkmarks View Post
    1. two numbers differ by 17. find the numbers that produce a minimum product.
    (i tried it out and my answer is -8.5 and 8.5, however i dont think that is right)
    x-y=17
    And you want to minimize,
    xy.

    Note, x=17+y

    Thus, you want to minimize,
    xy=(17+y)y=y^2+17y

    The minimum value occurs at -b/2a=-17/2=-8.5
    Then x=8.5

    Thus it seems correct.
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