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Math Help - factorizing ehh :(

  1. #1
    Super Member
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    Oct 2007
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    Santiago
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    517

    factorizing ehh :(

    hey guys, just doin a lil study..im a little confused about these questions.

    factor these two questions:

    1)
    <br />
81x^2 - 16y^2<br />

    2)
    <br />
(y+3)^3 + 8<br />

    any ideas?
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  2. #2
    Newbie
    Joined
    Mar 2008
    Posts
    5
    1. This is a product of 2 squares .

    <br /> <br />
81x^2 - 16y^2 = (9x - 4y)(9x + 4y)<br />

    2. Multiply out the brackets and add the 8. Then factorise:

    <br /> <br />
(y+3)^3 + 8 = y^3 + 9y^2 + 27y + 35 = (y+5)(y^2+4y+7)<br />

    Hope this helps.
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  3. #3
    Member
    Joined
    Feb 2008
    From
    Westwood, Los Angeles, CA
    Posts
    176
    Thanks
    1
    Considering that you seem to be focusing on difference of squares, sum and difference of cubes, the intention is probably, for #2, that you recognize that (y+3)^3 + 8 is a difference of cubes and use that formula (where a = (y + 3), b = 2). You can do it the other way - multiply it all out - as well.
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