Results 1 to 4 of 4

Math Help - Factorise help

  1. #1
    Newbie
    Joined
    Jun 2009
    Posts
    1

    Factorise help

    Could you please help me factorise this expression:

    4x^2+2x-20
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Behold, the power of SARDINES!
    TheEmptySet's Avatar
    Joined
    Feb 2008
    From
    Yuma, AZ, USA
    Posts
    3,764
    Thanks
    78
    Quote Originally Posted by lilly View Post
    Could you please help me factorise this expression:

    4x^2+2x-20

    Well there are many different ways to do this, but here is one...

    For any quadratic ax^2+bx+c multiply a and c together to get

    a\cdot c =4\cdot (-20)=-80

    Now we need to find factors of the above that add up to b

    b=2 and note that -8 \cdot 10=-80 \mbox{ and }-8+10=2

    So now we rewrite the b term as the sum above i.e

    2x=-8x+10x to get

    4x^2-8x+10x-20 now group the first and last two terms to get

    4x^2-8x+10x-20 \iff (4x^2-8x)+(10x-20)

    Now factor each grouping

    4x(x-2)+10(x-2) = (x-2)(4x+10)=2(x-2)(2x+5)
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member
    Joined
    May 2009
    Posts
    527
    Interesting... this is the same question as in
    http://www.mathhelpforum.com/math-he...rise-help.html
    And both of the original posters are from the same country. Coincidence?


    01
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor

    Joined
    Apr 2005
    Posts
    15,405
    Thanks
    1328
    Are you suggesting that a person would post the same question twice?

    Surely not!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Factorise.
    Posted in the Algebra Forum
    Replies: 4
    Last Post: April 26th 2011, 04:07 AM
  2. Factorise
    Posted in the Algebra Forum
    Replies: 3
    Last Post: April 11th 2010, 10:48 PM
  3. factorise
    Posted in the Algebra Forum
    Replies: 2
    Last Post: February 25th 2010, 01:27 AM
  4. should this factorise?
    Posted in the Trigonometry Forum
    Replies: 4
    Last Post: February 15th 2010, 10:14 PM
  5. Factorise :/
    Posted in the Algebra Forum
    Replies: 2
    Last Post: January 6th 2010, 12:01 PM

Search Tags


/mathhelpforum @mathhelpforum