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Math Help - need help plz, factoring

  1. #1
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    need help plz, factoring

    i have two problems like this


    6y^2+y-15



    but whenever i try to factor it i always get prime so could you guys just like give me an example or something similar to that problem because i cant find anything about that in my notes thank you
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  2. #2
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    Quote Originally Posted by elfen_lied View Post
    i have two problems like this


    6y^2+y-15



    but whenever i try to factor it i always get prime so could you guys just like give me an example or something similar to that problem because i cant find anything about that in my notes thank you
    (2*y - 3)*(3*y + 5)
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  3. #3
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    Quote Originally Posted by AfterShock View Post
    (2*y - 3)*(3*y + 5)
    uh.....whats that?????
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  4. #4
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    Quote Originally Posted by elfen_lied View Post
    uh.....whats that?????
    You asked how to factor 6*y^2+y-15, which is:

    (2*y - 3)*(3*y + 5)

    If you expand it by using FOIL, you will see it is 6*y^2+y-15:

    [(2y*3y) + (2y*5) + (-3*3y) + (-3*5)] = 6y^2 + 10 y - 9y -15 = 6y^2 + y - 15

    EDIT: editted to show more steps.
    Last edited by AfterShock; December 6th 2006 at 10:34 PM.
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  5. #5
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    Quote Originally Posted by AfterShock View Post
    You asked how to factor 6*y^2+y-15, which is:

    (2*y - 3)*(3*y + 5)

    If you expand it by using FOIL, you will see it is 6*y^2+y-15:

    [(2y*3y) + (2y*5) + (-3*3y) + (-3*5)] = 6y^2 + 10 y - 9y -15 = 6y^2 + y - 15

    EDIT: editted to show more steps.

    uh can u show me how you got it?
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  6. #6
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    Quote Originally Posted by elfen_lied View Post
    uh can u show me how you got it?
    Intuition. At your level, you will want to do a lot of guessing and checking, as I explain below.

    Well, Wikipedia can probably explain it better than I could. Take a look at:

    Factorization - Wikipedia, the free encyclopedia

    I can just look at the problem and immediately see that it factors to that. You want your middle and outer terms to equal y (in this case -9y + 10y) and you want to make sure you have degree 2 (y^2). Specifically, you want 6y^2, therefore will want the first terms of each composition to be either:

    1, 6
    6, 1
    3, 2
    2, 3

    And finally you want the 2nd terms of each composition to equal -15; thus, this will help you determine which of the combinations above you need to factor the whole expression, since you want the 6y^2 and -y to be fixed.

    It takes practice.
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