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Math Help - expanding brackets

  1. #1
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    multiplication

    hi, i need to expand these brackets expanding brackets-untitled1.jpg, i know the answer will be 20 but i need to know what expanding brackets-untitled2.jpg=
    Last edited by andyboy179; January 18th 2010 at 09:44 AM.
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  2. #2
    Super Member bigwave's Avatar
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    Quote Originally Posted by andyboy179 View Post
    hi, i need to expand these brackets Click image for larger version. 

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ID:	14875, i know the answer will be 20 but i need to know what Click image for larger version. 

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    (2-4\sqrt{3})(2+4\sqrt{3}) \Rightarrow  2^2 - (4\sqrt{3})^2  \Rightarrow 4-48 = -44

    -2\times4\sqrt{3} = -8\sqrt{3}

    Edit:apparently I didn't go down the right path with this, as per definition of "expansion"
    Last edited by bigwave; January 18th 2010 at 03:19 PM. Reason: direction
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  3. #3
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    at school we are told to work it out like this, (the blank spaces are the ones i don't know) expanding brackets-untitled3.jpg
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  4. #4
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    RULE: (x + y)(x - y) = x^2 - y^2

    By the way, that's not "expanding brackets": it's a multiplication.
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  5. #5
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    Quote Originally Posted by andyboy179 View Post
    at school we are told to work it out like this, (the blank spaces are the ones i don't know) Click image for larger version. 

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    I don't follow that "method";
    BUT 4sqrt(3) times 4sqrt(3) = 48, not 24
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  6. #6
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    Quote Originally Posted by Wilmer View Post
    I don't follow that "method";
    BUT 4sqrt(3) times 4sqrt(3) = 48, not 24
    oh ye, i know what i did wrong! so what would -2 x 4sqrt(3)= ?
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  7. #7
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    Quote Originally Posted by andyboy179 View Post
    oh ye, i know what i did wrong! so what would -2 x 4sqrt(3)= ?
    Doesn't matter, because you also need to do +2 x 4sqrt(3), so the
    2 will result in zero.
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  8. #8
    No one in Particular VonNemo19's Avatar
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    Quote Originally Posted by andyboy179 View Post
    at school we are told to work it out like this, (the blank spaces are the ones i don't know) Click image for larger version. 

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    The method that you use in school, although correct, is not the method used by most (and when I say most-I mean almost all) institutions. A really good explaination of how these problems are done can be found here.

    algebra.help -- Simplifying using the FOIL Method

    BTW: Your method is not an "expansion" in the normal sense of the word, as someone has already mentioned. THe term expansion implies that there will be more terms after the mutiplication is complete (in most cases). And that thes terms may have likenesses.
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