Results 1 to 4 of 4

Math Help - havent a clue!

  1. #1
    Newbie
    Joined
    Dec 2007
    From
    U.K
    Posts
    21

    havent a clue!

    havent a clue!

    6x2+x-15=0
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    10,212
    Thanks
    419
    Awards
    1
    Quote Originally Posted by jenko View Post
    havent a clue!

    6x2+x-15=0
    Let's try this using the method I posted in your other thread.

    Mulitply 6 and -15: -90

    Now list all pairs of factors of -90:
    1, -90
    2, -45
    3, -30
    6, -15
    9, -10
    10, -9
    15, -6
    30, -3
    45, -2
    90, -1

    Now which of these pairs add to 1? The 10 and -9, of course. So 1 = 10 - 9:
    6x^2 + x - 15 = 0

    6x^2 + (10 - 9)x - 15 = 0

    6x^2 + 10x - 9x - 15 = 0

    (6x^2 + 10x) + (-9x - 15) = 0

    2x(3x + 5) - 3(3x + 5) = 0

    (2x - 3)(3x + 5) = 0

    So set each factor equal to 0:
    2x - 3 = 0 \implies x = \frac{3}{2}
    or
    3x + 5 = 0 \implies x = -\frac{5}{3}

    -Dan
    Follow Math Help Forum on Facebook and Google+

  3. #3
    GAMMA Mathematics
    colby2152's Avatar
    Joined
    Nov 2007
    From
    Alexandria, VA
    Posts
    1,172
    Awards
    1
    BTW, after a lot of practice of factorials, you will be able to look at them for a couple seconds and know what the constants will be.

    I understand your plight. When I was a kid learning about factoring, my teacher didn't even show me about the additives and multiples that make up the constants right away. Needless to say, I taught it to myself.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Dec 2007
    From
    U.K
    Posts
    21
    i know the basics of mathematics e.g multiples etc it jus some of the terminologies that are used which i have never heared of or are unsure of ite been a while since i have done this last time i done then wen i was in high school two years ago and ever since that day i forgot it all as i thought i would never use it on it later life which i realy regret otherwise i wouldnt be here now or better still would be here with even more harder questions for you guys to help me with!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. What is the clue to think that way?
    Posted in the Algebra Forum
    Replies: 3
    Last Post: January 4th 2011, 02:47 AM
  2. Matrices Question - Check i havent gone insane
    Posted in the Calculus Forum
    Replies: 1
    Last Post: February 4th 2010, 04:14 AM
  3. Need help please have no clue
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: November 5th 2008, 07:11 PM
  4. My sister is in need and i havent a clue.
    Posted in the Algebra Forum
    Replies: 1
    Last Post: October 28th 2007, 03:04 PM
  5. Don't Have A Clue!!
    Posted in the Business Math Forum
    Replies: 1
    Last Post: November 28th 2006, 06:10 PM

Search Tags


/mathhelpforum @mathhelpforum