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Math Help - Simple Factoring question that is bugging me

  1. #1
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    Simple Factoring question that is bugging me

    I'm trying to factor

    s^3 + 3s^2 + 3s + 1

    From pascals triangle I know the answer by looking at it. But when I go to try and factor it showing all work I get stumped.. I can't seem to get (s + 1)^3 when factoring the long way and not just by looking at it.

    I've tried grouping, long division, I can't get it. Can anyone show me what I'm missing?
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  2. #2
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    Quote Originally Posted by Charles Dexter Ward View Post
    I'm trying to factor

    s^3 + 3s^2 + 3s + 1

    From pascals triangle I know the answer by looking at it. But when I go to try and factor it showing all work I get stumped.. I can't seem to get (s + 1)^3 when factoring the long way and not just by looking at it.

    I've tried grouping, long division, I can't get it. Can anyone show me what I'm missing?
    s^3 + 3s^2 + 3s + 1

    = s^3 + (2s^2 + s^2) + (2s + s) + 1

    = (s^3 + 2s^2 + s) + (s^2 + 2s + 1)

    = s(s^2 + 2s + 1) + (s^2 + 2s + 1)

    = (s + 1)(s^2 + 2s + 1) = (s + 1)(s + 1)^2 = (s + 1)^3
    but you'd probably have to be psychic to see something like that in a more complicated example.

    Of course, you can always use the rational root theorem.

    -Dan
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  3. #3
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    ahhh, I didn't think about splitting up the s^2 and s like that. Tricky!

    ahh I see I was trying to use the rational root theorem( I wasn't aware of it's name before now though ) I just messed up with dividing by s + 1. I also see that I wasn't properly finding the roots, though it just happened to work out this time because the leading coefficient is 1. I wasn't aware of p / n. I was only using the numbers the constant was divisible by.

    Thanks for the help, I appreciate it!
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