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Thread: multiplying binomial w/two trinomials

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    multiplying binomial w/two trinomials

    Sorry, I figured it out; I'd like to delete the thread can't seem to delete right now though.
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    Quote Originally Posted by greatsheelephant View Post
    Here is the expression I'm supposed to find the product of:
    $\displaystyle (4y^3+5y^2-12y)(-12-2)(7y^2-9y+12)$

    To multiply it, does it matter whether or not I multiple a binomial with one of the trinomials first, or should I multiply the two trinomials together first? I can't seem to get it right. First I tried multiplying on eof the trinomials with the binomial:
    $\displaystyle -12y(4y^3+5y^2-12y)-2(4y^3+5y^2-12y)$
    which gave me $\displaystyle -48y^4+76y^3-10y^2+24$
    I then multiplied that by the other trinomial,
    $\displaystyle (7y^2-9y+12)$
    which gave me $\displaystyle -336y^6+964y^5-1330y^4+1002y^3+48y^2-216y+288$

    the correct answer is supposed to be $\displaystyle -336y^6-44y^5+974y^4-1854y^3+1392y^2+288y$

    Thanks
    $\displaystyle -12-2 = -14$ so that's the middle bracket sorted. Also you can take a factor of y from the first set.

    $\displaystyle -14y(4y^2+5y-12)(7y^2-9y+12)$

    Since this gives a polynomial of order 5 whereas the book says order 6 I suspect you've made a typo in the original question. Probably the middle bracket
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