Page 2 of 2 FirstFirst 12
Results 16 to 27 of 27

Math Help - Factorise (m+1)^2 - 9

  1. #16
    MHF Contributor Unknown008's Avatar
    Joined
    May 2010
    From
    Mauritius
    Posts
    1,260
    Quote Originally Posted by FailInMaths View Post
    I have only learn that: ( For Factorise )

    1) (a)square + 2ab + (b)square = (a+b)square
    2) (a)square - 2ab + (b)square = (a-b)square
    3) (a)square - (b)square = (a+b)(a-b)
    Ok, but this problem is one where those cannot be applied when you subtract the 9. You have different factors.
    Follow Math Help Forum on Facebook and Google+

  2. #17
    Member
    Joined
    Jan 2011
    Posts
    104
    Quote Originally Posted by Unknown008 View Post
    If a is m, and b is 4...

    m^2 +2m-8

    How can you replace m by a and 4 by b here?

    Like this?

    a^2 +2a-2b

    This doesn't bring to (a-b)(a+b)

    Like this?

    a^2 +\dfrac{ba}{2}-\dfrac{b^2}{2}

    That neither.

    In short, no. If you ever got m^2 - 9 for example, then it would be m^2 - 9 = (m+3)(m-3). But that is not the case.
    Hi, can you show me the steps you do to obtain the answer completely? Maybe from there i can understand how things work, cause i just can't seem to comprehend what you guys said, sorry man, i am not advance, seek your understanding
    Follow Math Help Forum on Facebook and Google+

  3. #18
    MHF Contributor Unknown008's Avatar
    Joined
    May 2010
    From
    Mauritius
    Posts
    1,260
    The full solution:

    (m+1)^2 - 9 = m^2 + 2m + 1 - 9

     = m^2 + 2m - 8

     = (m+4)(m-2)
    Follow Math Help Forum on Facebook and Google+

  4. #19
    Member
    Joined
    Jan 2011
    Posts
    104
    Quote Originally Posted by Unknown008 View Post
    The full solution:

    (m+1)^2 - 9 = m^2 + 2m + 1 - 9

     = m^2 + 2m - 8

     = (m+4)(m-2)
    Got it, Thanks so much
    Follow Math Help Forum on Facebook and Google+

  5. #20
    Newbie
    Joined
    Feb 2011
    Posts
    7
    This is very simple.
    Just expand it out.
    you should get m2+2m+1-9 = m2+2m-8
    After that factorise it.
    Answer should be (m+4)(m-2)
    Follow Math Help Forum on Facebook and Google+

  6. #21
    Newbie
    Joined
    Feb 2011
    Posts
    7
    Quote Originally Posted by FailInMaths View Post
    Factorise
    (m+1)Square -9

    My answer : (m-8)(m+8)

    And also, is it true that we can't write capital letters for algebra? only small letters.

    Thanks so much for helping!
    Or you could use differnce of 2 squares.
    Because (m+1)Square - (3) Square.
    Put in the forumala (a+b)(a-b)
    Follow Math Help Forum on Facebook and Google+

  7. #22
    Member
    Joined
    Jan 2011
    Posts
    104
    Quote Originally Posted by Calye View Post
    Or you could use differnce of 2 squares.
    Because (m+1)Square - (3) Square.
    Put in the forumala (a+b)(a-b)
    Yeah, i got it already, in another post, Thanks so much =)
    Follow Math Help Forum on Facebook and Google+

  8. #23
    Newbie
    Joined
    Feb 2011
    Posts
    7
    No problem.
    Glad to help.
    Follow Math Help Forum on Facebook and Google+

  9. #24
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by FailInMaths View Post
    Factorise
    (m+1)Square -9

    My answer : (m-8)(m+8)

    And also, is it true that we can't write capital letters for algebra? only small letters.

    Thanks so much for helping!
    I realise you think you know how to do this particular question now. However, recognising a difference of two squares should have been the prefered method of solution right from the get-go in my opinion.

    A^2 - B^2 = (A - B)(A + B) and in your case A = m + 1 and B = 3.

    Expanding and factorising takes a lot more time, requires more skill and introduces far greater opportunity for error.
    Follow Math Help Forum on Facebook and Google+

  10. #25
    MHF Contributor
    Joined
    Dec 2007
    From
    Ottawa, Canada
    Posts
    3,102
    Thanks
    68
    Convince yourself that a^2 - 9 = (a + 3)(a - 3)

    (m + 1)^2 - 9 = ?
    Let a = m + 1
    a^2 - 9
    = (a + 3)(a - 3)
    Now substitute back in:
    (m + 1 + 3)(m + 1 - 3)
    = (m + 4)(m - 2)
    Follow Math Help Forum on Facebook and Google+

  11. #26
    Newbie
    Joined
    Feb 2011
    Posts
    17
    Right. Here (m+1)^2 is 'a' and 9 is 'b'. So put that in identity a^2-b^2=(a+b)(a-b). what you will get is:
    (m+1)^2-(3)^2
    =[(m+1)+3][(m+1)-3]
    =(m+4)(m-2)
    this is your solution.
    Follow Math Help Forum on Facebook and Google+

  12. #27
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by amey View Post
    Right. Here (m+1)^2 is 'a' and 9 is 'b'. So put that in identity a^2-b^2=(a+b)(a-b). what you will get is:
    (m+1)^2-(3)^2
    =[(m+1)+3][(m+1)-3]
    =(m+4)(m-2)
    this is your solution.
    So many replies saying exactly the same thing as all the others. Thread closed.
    Follow Math Help Forum on Facebook and Google+

Page 2 of 2 FirstFirst 12

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

/mathhelpforum @mathhelpforum