Results 1 to 4 of 4

Math Help - Finding zeros after using synthetic division.

  1. #1
    Junior Member
    Joined
    Apr 2008
    Posts
    27

    Finding zeros after using synthetic division.

    Use synthetic division to divide g(x)=x^3-17x^2+90x-144 by x-8. Use the result to find all zeros of g.

    I got x^2-9x+12 for the quotient with -48 remainder.

    Is this correct?
    The problem is, how am I supposed to find all zeros when the divisor I am expected to use has a remainder? By the way the question is worded, do you think I am supposed to find a divisor that works?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member
    Joined
    Feb 2008
    From
    Berkeley, Illinois
    Posts
    364
    Quote Originally Posted by theevilp0ptart View Post
    Use synthetic division to divide g(x)=x^3-17x^2+90x-144 by x-8. Use the result to find all zeros of g.

    I got x^2-9x+12 for the quotient with -48 remainder.

    Is this correct?
    The problem is, how am I supposed to find all zeros when the divisor I am expected to use has a remainder? By the way the question is worded, do you think I am supposed to find a divisor that works?
    theevil,

    The roots for your cubic are 3, 6, and 8. I got that from here:

    Soving Cubic Equations

    Your discriminant was less than 0, which means the cubic has 3 real unique roots.

    Since you want to divide by x - 8, you can use the synthetic division calculator I posted in the computer software forum also located here:

    Synthetic Division

    Dividing your cubic by (x - 8), I get x^2 - 9x + 18

    That's a quadratic equation that you can easily solve for your last 2 roots.

    Check out the math for the synthetic division to see where you went astray. Based on how close you and I are, I bet it was your last step in the constant column for synthetic division.

    Let me know if you have questions.
    Last edited by mathceleb; April 4th 2009 at 09:09 AM.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Apr 2008
    Posts
    27
    Quote Originally Posted by mathceleb View Post
    theevil,

    The roots for your cubic are 3, 6, and 8. I got that from here:

    Soving Cubic Equations

    Your discriminant was less than 0, which means the cubic has 3 real unique roots.

    Since you want to divide by x - 8, you can use the synthetic division calculator I posted in the computer software forum also located here:

    Synthetic Division

    Dividing your cubic by (x - 8), I get x^2 - 9x + 18

    That's a quadratic equation that you can easily solve for your last 2 roots.

    Check out the math for the synthetic division to see where you went astray. Based on how close you and I are, I bet it was your last step in the constant column for synthetic division.

    Let me know if you have questions.
    Oh... I see I made I simple math mistake in my addition. That changed the whole problem. Thank you for the help!
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor Mathstud28's Avatar
    Joined
    Mar 2008
    From
    Pennsylvania
    Posts
    3,641

    Just to let you know

    if you get a remainder when synthetically dividing it means that your divisor is not a proper divisor(not sure if these terms work for polynomials) of your polynomial
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Synthetic division (Finding all zeros)
    Posted in the Pre-Calculus Forum
    Replies: 6
    Last Post: October 14th 2009, 02:10 PM
  2. Polynomial division vs synthetic division
    Posted in the Algebra Forum
    Replies: 2
    Last Post: April 9th 2009, 06:49 AM
  3. synthetic division
    Posted in the Algebra Forum
    Replies: 3
    Last Post: January 11th 2009, 06:12 PM
  4. Synthetic Division
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: October 30th 2007, 03:22 PM
  5. Zeros and Synthetic Division
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: December 5th 2005, 10:32 PM

Search Tags


/mathhelpforum @mathhelpforum