Results 1 to 6 of 6

Math Help - Find the Larger Integer

  1. #1
    Banned
    Joined
    Aug 2009
    From
    USA
    Posts
    126

    Find the Larger Integer

    The product of two integers is -40. If the same two integers are added, their sum is -3. Find the larger of the integers.

    I did this:

    x*y = -40...Equation A
    x + y = -3..Equation B

    I solved Equation B for y and got y = -x - 3.

    I plugged the value for y into Equation A and solved for x.

    x(-x - 3) = -3

    -x^2 - 3x = -3

    I moved everything to the right side.

    0 = x^2 + 3x - 40

    My final answer is 5 but the math book tells me that the correct answer is -8. Can you explain who is right and why?

    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member Matt Westwood's Avatar
    Joined
    Jul 2008
    From
    Reading, UK
    Posts
    737
    Thanks
    1
    Depends on whether they mean "largest" in the sense of "absolute value" (in which case it's -8) or "largest" in the sense of "most positive". Go back thru the book and see how they define "largest".
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,605
    Thanks
    1573
    Awards
    1
    Quote Originally Posted by sharkman View Post
    The product of two integers is -40. If the same two integers are added, their sum is -3. Find the larger of the integers.

    I did this:

    x*y = -40...Equation A
    x + y = -3..Equation B

    I solved Equation B for y and got y = -x - 3.

    I plugged the value for y into Equation A and solved for x.

    x(-x - 3) = -40

    -x^2 - 3x = -3

    I moved everything to the right side.

    0 = x^2 + 3x - 40

    My final answer is 5 but the math book tells me that the correct answer is -8. Can you explain who is right and why?
    Note the minor correction above.
    But, yes you are correct.

    EDIT: I think that "largest" means largest.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Banned
    Joined
    Aug 2009
    From
    USA
    Posts
    126

    ok but...

    Quote Originally Posted by Plato View Post
    Note the minor correction above.
    But, yes you are correct.

    EDIT: I think that "largest" means largest.
    Are you saying that the equation x(-x - 3) = -40should not be equated to -40? But the question stated that the product of two integers is -40. I moved everything to the right side and so -40 remains -40, right? Please, explain what you meant by "minor correction" in your reply. Thank you.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,605
    Thanks
    1573
    Awards
    1
    Quote Originally Posted by sharkman View Post
    Are you saying that the equation x(-x - 3) = -40should not be equated to -40? But the question stated that the product of two integers is -40. I moved everything to the right side and so -40 remains -40, right? Please, explain what you meant by "minor correction" in your reply. Thank you.
    Look at your OP.
    You had \color{red}x(-x-3)=-3.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Banned
    Joined
    Aug 2009
    From
    USA
    Posts
    126

    ok...

    Quote Originally Posted by Plato View Post
    Look at your OP.
    You had \color{red}x(-x-3)=-3.
    I finally see the typo. Thank you.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 13
    Last Post: August 3rd 2010, 03:16 AM
  2. Find the Smallest Integer
    Posted in the Algebra Forum
    Replies: 2
    Last Post: August 10th 2009, 01:24 PM
  3. Find Larger Number
    Posted in the Algebra Forum
    Replies: 3
    Last Post: April 21st 2009, 09:04 PM
  4. Find Next Integer
    Posted in the Number Theory Forum
    Replies: 3
    Last Post: January 24th 2007, 11:26 AM
  5. Find Larger Number
    Posted in the Math Topics Forum
    Replies: 2
    Last Post: January 19th 2007, 12:45 PM

Search Tags


/mathhelpforum @mathhelpforum