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Factorising

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    (Original post by zed963)
    So the above is right,

    So if i had this expression : 6y(x+3y)+9(x+3y)^2

    Would that be (x+3y) and something which I can't figure out HELP
    Relax. Take a deep breathe. Now...

    6y(x+3y)+9(x+3y)(x+3y)

    (x+3y) - Common Factor.

    6y(x+3y)+9(x+3y)(x+3y)

    Now continue...
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    (Original post by TenOfThem)
    Yes

    What you have there is

    6y(x+3y) + 9(x+3y)(x+3y)

    Take out the red and what is left ... that is your other bracket
    9y +9 + x
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    (Original post by zed963)
    9y +9 + x
    I am sorry but I am going to bow out now

    You need to ask you teacher because you need someone sat next to you pointing to brackets, crossing things out, asking you questions

    There is a major gap in your understanding here and you need someone to help properly

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    (Original post by Math12345)
    Relax. Take a deep breathe. Now...

    6y(x+3y)+9(x+3y)(x+3y)

    (x+3y) - Common Factor.

    6y(x+3y)+9(x+3y)(x+3y)

    Now continue...
    why have u crossed the 9 out
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    (Original post by zed963)
    why have u crossed the 9 out
    Look carefully.
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    (Original post by zed963)
    9y +9 + x
    6y(x+3y)+9(x+3y)(x+3y)

    Remove the common factor I have crossed out and you are left with:

    6y+9(x+3y)
    6y+9x+27y

    There's your second bit.
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    (Original post by zed963)
    why have u crossed the 9 out

    (Original post by Math12345)
    Look carefully.
    i thought the exact same thing, the 9 isn't crossed out, just how the 9 is displayed next to something that IS crossed out, makes it look like it is crossed out.

    As TenOfThem said, you really need to go and see a teacher, or even ask a friend for some help. With these sort of things, you do need people to point it out to you, otherwise you'll just keep posting question after question.
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    (Original post by Math12345)
    6y(x+3y)+9(x+3y)(x+3y)

    Remove the common factor I have crossed out and you are left with:

    6y+9(x+3y)
    6y+9x+27y

    There's your second bit.
    So that would be 3(3x+11y)
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    (Original post by zed963)
    So that would be 3(3x+11y)
    Leave it as (9x+33y).
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    (Original post by zed963)
    So that would be 3(3x+11y)
    But in the answer sheet it give 3(x+y)(3x+11y)
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    (Original post by zed963)
    But in the answer sheet it give 3(x+y)(3x+11y)
    wouldn't matter. Either is correct.
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    (Original post by zed963)
    But in the answer sheet it give 3(x+y)(3x+11y)
    Talk to a teacher, because I don't think you get it completely.
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    (Original post by Math12345)
    Talk to a teacher, because I don't think you get it completely.
    but the common factor of 6 and 9 is three
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    (Original post by zed963)
    but the common factor of 6 and 9 is three
    Yes, but I still think you don't know how to get there.

    Practice a few more questions.
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    (Original post by Math12345)
    Yes, but I still think you don't know how to get there.

    Practice a few more questions.
    Have you got anymore questions?
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    (Original post by zed963)
    Have you got anymore questions?
    No, I suggest you ask your teacher first for a good detailed explanation then ask them for questions.
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    Hi, I'm going to hijack this thread cos the topic is pretty similar. I'm self-teaching A-level and I unfortunately think I have missed something basic in factorising skills that keeps bringing me to a dead stop. It happens when the coefficient of x^2 is particularly high, especially when the resulting ac is large and negative. This is the problem that has just confused me at this point:

    16x^2 + 16x - 45

    I couldn't work out for the life of me any numbers that worked and when I checked the answer is (4x + 9)(4x - 5). I get that there was (probably?) a (16x + 36)(16x - 20) stage but I don't think I could ever have got to it by myself.

    How do I go about finding the right figures? It's worst when b is positive and ac is negative, is there a method or a stage to the method I have missed to make it easier to figure out correctly? Thanks a lot for any help.
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    Realised just now that this thread is marked as Secondary School maths so I'm going to try bumping it this one time and if that fails I'll make my own thread with the above question.
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    (Original post by Ronove)
    Hi, I'm going to hijack this thread cos the topic is pretty similar. I'm self-teaching A-level and I unfortunately think I have missed something basic in factorising skills that keeps bringing me to a dead stop. It happens when the coefficient of x^2 is particularly high, especially when the resulting ac is large and negative. This is the problem that has just confused me at this point:

    16x^2 + 16x - 45

    I couldn't work out for the life of me any numbers that worked and when I checked the answer is (4x + 9)(4x - 5). I get that there was (probably?) a (16x + 36)(16x - 20) stage but I don't think I could ever have got to it by myself.

    How do I go about finding the right figures? It's worst when b is positive and ac is negative, is there a method or a stage to the method I have missed to make it easier to figure out correctly? Thanks a lot for any help.
    With those, I think you just have to 'see' it. Maybe someone has a better method (EDIT: Turns out Maths12345 does ), but if you can't see it then I'd just complete the square.
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    (Original post by Ronove)
    Hi, I'm going to hijack this thread cos the topic is pretty similar. I'm self-teaching A-level and I unfortunately think I have missed something basic in factorising skills that keeps bringing me to a dead stop. It happens when the coefficient of x^2 is particularly high, especially when the resulting ac is large and negative. This is the problem that has just confused me at this point:

    16x^2 + 16x - 45

    I couldn't work out for the life of me any numbers that worked and when I checked the answer is (4x + 9)(4x - 5). I get that there was (probably?) a (16x + 36)(16x - 20) stage but I don't think I could ever have got to it by myself.

    How do I go about finding the right figures? It's worst when b is positive and ac is negative, is there a method or a stage to the method I have missed to make it easier to figure out correctly? Thanks a lot for any help.
    First thing to always check is if you can simplify the equation. In this case you can't.

    16x^2+16x-45

    The product is a*c: 16*-45=-720
    The sum is b: +16

    What 2 numbers give a product of -720 and a sum of +16?

    36 and -20.

    Now split the b term into this: (you should put it in a order, so you can factorise e.g. 16 and 36 (have 4 in common) and 20 and 45 (have 5 in common).

    16x^2+36x-20x-45

    Factorise


    4x(4x+9)-5(4x+9)

    Common factor?

    (4x+9)

    Next bracket is the bits left over.

    (4x-5)

    Answer:

    (4x+9)(4x-5)

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Updated: April 15, 2012
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