Results 1 to 5 of 5

Math Help - Finding the sum+product of a quadratic equation's roots?

  1. #1
    Junior Member
    Joined
    Jan 2008
    Posts
    53

    Finding the sum+product of a quadratic equation's roots?

    I wasn't really paying attention in class, and im having trouble. Heres the question:

    For each quadratic equation, find: a) the sum of its roots and b) the product of its roots

    x^2-2x-15=0

    Ik in order to find the sum of the roots you need to do: \frac{-b}{a} and for the product: \frac{c}{a}
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor Mathstud28's Avatar
    Joined
    Mar 2008
    From
    Pennsylvania
    Posts
    3,641
    Quote Originally Posted by eh501 View Post
    I wasn't really paying attention in class, and im having trouble. Heres the question:

    For each quadratic equation, find: a) the sum of its roots and b) the product of its roots

    x^2-2x-15=0

    Ik in order to find the sum of the roots you need to do: \frac{-b}{a} and for the product: \frac{c}{a}
    Factoring we get (x-5)(x+3)=0\Rightarrow{x=5,x=-3} therefore the sum of its roots is 2 and its product is -15
    Last edited by Mathstud28; April 21st 2008 at 05:13 PM.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Jan 2008
    Posts
    53
    Im sorry what?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor Mathstud28's Avatar
    Joined
    Mar 2008
    From
    Pennsylvania
    Posts
    3,641
    Quote Originally Posted by eh501 View Post
    Im sorry what?
    Sorry I made a typo so it didnt register...look now
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Moo
    Moo is offline
    A Cute Angle Moo's Avatar
    Joined
    Mar 2008
    From
    P(I'm here)=1/3, P(I'm there)=t+1/3
    Posts
    5,618
    Thanks
    6
    Well...

    Here, a=1, b=-2, c=-15

    The sum of its roots would be \frac{2}{1}=2 and the product would be \frac{-15}{1}=-15

    This is the only thing you're asked (unless you didn't copied everything)

    -------

    If a_1 and a_2 are the roots, hence :

    a_1+a_2=2

    a_1 a_2=-15

    It's better than factorizing from who knows where
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Finding the roots of a Quadratic equation.
    Posted in the Algebra Forum
    Replies: 10
    Last Post: December 30th 2011, 01:42 PM
  2. Replies: 10
    Last Post: May 4th 2011, 08:42 AM
  3. Replies: 3
    Last Post: March 11th 2011, 07:27 PM
  4. Replies: 4
    Last Post: October 17th 2010, 07:36 AM
  5. Finding integer roots of quadratic
    Posted in the Algebra Forum
    Replies: 4
    Last Post: December 20th 2009, 09:39 AM

Search Tags


/mathhelpforum @mathhelpforum