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    sonam12's Avatar
    sonam12 Posts: 1, Reputation: 1
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    #1

    Sep 11, 2011, 08:07 PM
    Quadratic equation and problem solving?
    Find two consecutive positive integers whose product is 380
    Eugeneus's Avatar
    Eugeneus Posts: 3, Reputation: 1
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    #2

    Sep 11, 2011, 10:28 PM
    The answer is 19 and 20.
    ~~~~~~~~~~~~~~~~~~~~~~~~

    Let A = the smaller integer.

    (A) * (A + 1) = 380
    Then A^2 + A = 380
    And then A^2 + A - 380 = 0

    Quadratic formula gives:

    A = [-1 + SqRt(1 + 1520)] / 2 -OR- A = [-1 - SqRt(1 + 1520)] / 2
    Then A = [-1 + SqRt(1521)] / 2 -OR- A = [-1 - SqRt(1521)] / 2
    Then A = [-1 + 39] / 2 -OR- A = [-1 - 39] / 2
    Then A = 38 / 2 -OR- A = -40 / 2
    Finally A = 19 -OR- A = -20

    Therefore the two consecutive integers are 19 and 20 OR -20 and -19; but the requiremet calls for positive integers. Therefore the answer is 19 and 20.
    ~~~~~~~~~~~~~~~~~~~~~~~~
    Unknown008's Avatar
    Unknown008 Posts: 8,076, Reputation: 723
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    #3

    Sep 12, 2011, 09:23 AM
    While your answer is good, you should not do the homework of someone. This is against the rules of the forum, since it has a major ethical issue.

    The asker gets the answer served on a gold plate and did no work. Only a small percent of the askers would actually read and learn the full workings, while the other big majority will never read the workings, take the answer and stay in the darkness for such questions.

    The usual way around is to help the asker find the answer himself/herself by providing good "hints" which will make him/her think and understand in the right direction.

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