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Thread: Pre-calc help pls

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    Aura's Avatar
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    Pre-calc help pls

    Pls help with my homework
    This is the question I'm doing. Will +rep for an explanation on how to do it properly.
    The answer is 18.


    The polynomial equation x^3 - ax^2 + bx - c = 0, where a, b, and c are integers, and it has 6 as on of its roots. According to the rational root theorem, what is the value of c?
    Last edited by Aura; 12-16-2016 at 12:49 AM.

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    screw it I am dumb
    Last edited by Stocking Anarchy; 12-16-2016 at 12:14 AM.

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    Aura (12-16-2016)

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    Quote Originally Posted by Stocking Anarchy View Post
    screw it I am dumb
    thanks for trying though you da MVP

    still need help

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    You sure the original Q is not

    x^3 - ax^2 + bx - c = 0 ?

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    Quote Originally Posted by Stocking Anarchy View Post
    You sure the original Q is not

    x^3 - ax^2 + bx - c = 0 ?
    Oops, yes, it was supposed to be, haha, thank youu


    Maybe it'll be easier to help now?!

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    Are we 100% sure the value of C is 18? @Aura
    Last edited by Byte; 12-16-2016 at 09:02 AM.

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    Quote Originally Posted by Revelation343 View Post
    Are we 100% sure the value of C is 18? @Aura
    Yeah, 100%. I have the answers, just not the process.

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    Quote Originally Posted by Aura View Post
    Yeah, 100%. I have the answers, just not the process.
    (x−1)(x−1)(x−6) = x^3−8x^2+13x−6

    That's why I was asking. I'll do some more thinking on it, it's confusing to me how to figure out the coefficients of the equation, and to use the rational root theorem, and use synthetic division without them. I feel like a piece of the question is missing.

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    Quote Originally Posted by Revelation343 View Post
    (x−1)(x−1)(x−6) = x^3−8x^2+13x−6

    That's why I was asking. I'll do some more thinking on it, it's confusing to me how to figure out the coefficients of the equation, and to use the rational root theorem, and use synthetic division without them. I feel like a piece of the question is missing.
    I asked my teacher and this is his explanation:
    Using the rational root theorem, c/1 has to equal 6 somehow. He said that 18 was the only answer that was even a factor of 6 (the other choices were 2, 3, and 9; I didn't think I had to include them in this thread though lol. That probably would've helped.)
    That was way easier than I thought. thanks for all of your help, though, guys.

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