Results 1 to 4 of 4

Thread: Sum and product of roots (help)

  1. #1
    New Member
    Join Date
    May 2018
    HSC
    2018
    Gender
    Male
    Posts
    2
    Rep Power
    1

    Lightbulb Sum and product of roots (help)

    Find the value of n in the equation 2x^2 -5(n-1)x +12=0 If two roots are consecutive.

    The answer in the book is n= -1 , 3

  2. #2
    Executive Member
    Join Date
    Jul 2014
    HSC
    2017
    Gender
    Female
    Posts
    1,808
    Rep Power
    5

    Re: Sum and product of roots (help)

    Let roots be alpha and alpha+1

    Sum of roots = 5(n-1)/2 = 2*alpha + 1

    Rearranging equation to have only n LHS, n = (2/5)(2*alpha + 1) + 1

    Prod. of roots = alpha(alpha + 1) = 6

    alpha^2 + alpha - 6 = 0

    Quadratic formula, alpha = -3 or 2.

    Subbing into n = ....

    n = -1 or 3.

  3. #3
    New Member
    Join Date
    May 2018
    HSC
    2018
    Gender
    Male
    Posts
    2
    Rep Power
    1

    Re: Sum and product of roots (help)

    is this the next step

    ( sub 2 into n )

    2x^2+5x+12=0

    =-5 root 5^2 - 4(2)(12)/4

    =-5 root 25 -96/4

    there is no solution

  4. #4
    Executive Member
    Join Date
    Jul 2014
    HSC
    2017
    Gender
    Female
    Posts
    1,808
    Rep Power
    5

    Re: Sum and product of roots (help)

    Quote Originally Posted by Saini View Post
    is this the next step

    ( sub 2 into n )

    2x^2+5x+12=0

    =-5 root 5^2 - 4(2)(12)/4

    =-5 root 25 -96/4

    there is no solution
    Let n = 2

    2/5 * (4 + 1) + 1

    = 3

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •