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Math Homework Help DESPERATLY NEEDED!!!

Discussion in 'Archive: Your Jedi Council Community' started by Liz Skywalker, Jan 8, 2002.

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  1. Liz Skywalker

    Liz Skywalker Ex-Mod star 6 VIP - Former Mod/RSA

    Registered:
    Jun 13, 2000
    okay, the problem is:

    X^5 - 81 = 0

    and we need to get the 5 answers.

    my friend thinks that the answers are the 5th root of 81, multiplicity of 5. but that hits me wrong.


    Can anyone help?
     
  2. AL

    AL Jedi Grand Master star 5

    Registered:
    Aug 22, 1998

    X to the power of 5 is 81, according to that calculation. It is pretty easy, you know.
     
  3. anakin_skywalker_sct

    anakin_skywalker_sct Jedi Master star 5

    Registered:
    Apr 18, 2001
    X^5 = 81

    er... can't get any further, sorry.
     
  4. Ardens_Furore

    Ardens_Furore Jedi Padawan star 4

    Registered:
    May 14, 2001
    I think by the Descartes rule of signs there is only one positive real root, 81^(1/5)

    There aren't any negative real roots.

    f(x) = x^5 - 81

    - One sign variation -> one positive real root or (1 - 2n) positive real roots where n can be any positive integer. Since that's less than 0, there should be one positive real root.

    f(-x) = (-x)^5 - 81
    f(-x) = -x^5 - 81

    - No sign variations -> no negative real roots or (0 - 2n) negative real roots where n can be any positive integer. It's also less than 0, so there are no negative real roots.

    EDIT: making sure there aren't any little mistakes.
     
  5. Stranded in space

    Stranded in space Jedi Padawan star 4

    Registered:
    Feb 13, 2000
    x is about 2.4596

    or

    5 = log base x 81

    can't think of anything else.
     
  6. Liz Skywalker

    Liz Skywalker Ex-Mod star 6 VIP - Former Mod/RSA

    Registered:
    Jun 13, 2000
    Ardens, yeah, that was what I was thinkgin. buit for the life of me I can't find the other ones. I'm doing an hour's worth of synthetic division right now...here's to it working. [face_plain]
     
  7. Lobot_Omy

    Lobot_Omy Moderator Emeritus star 6 VIP - Former Mod/RSA

    Registered:
    Jul 9, 2001
    Ummm, I'm pretty sure you aren't supposed to spend that much time on one homework problem. When a problem is taking that long it usually means there's something wrong with the problem or you've missed something in the description. Or maybe made a simple error in your work and now everything is off.

    Like the other people said, there doesn't seem to be any way to factor it, so it's 81^(1/5).

    Try looking over the steps you made leading up to that point, maybe you've made an arithmetical error. That's where I usually make mistakes.
     
  8. Liz Skywalker

    Liz Skywalker Ex-Mod star 6 VIP - Former Mod/RSA

    Registered:
    Jun 13, 2000
    the question say:

    "Find all real and immaginary solutions to the following equations:

    #8: x^5 - 81 = 0"


    that's the problem. and I don't know where to go from there after making it

    x^5 = 81


    [face_plain]
     
  9. Just_A_Slacker

    Just_A_Slacker Jedi Youngling star 4

    Registered:
    Aug 4, 2001
    See, this is why I am not alone in saying Math Sucks!
     
  10. neimoidian_85

    neimoidian_85 Jedi Padawan star 4

    Registered:
    Dec 30, 1999
    What is the name of your math class?
     
  11. Liz Skywalker

    Liz Skywalker Ex-Mod star 6 VIP - Former Mod/RSA

    Registered:
    Jun 13, 2000
    Pre-Calculus...
     
  12. Terra

    Terra Jedi Padawan star 4

    Registered:
    Oct 25, 2000
    I agree with Just_A_Slacker!
     
  13. Terra

    Terra Jedi Padawan star 4

    Registered:
    Oct 25, 2000
    Oh, as well as anything said by a clever person.
     
  14. neimoidian_85

    neimoidian_85 Jedi Padawan star 4

    Registered:
    Dec 30, 1999
    Pre-calculus.........MWAHAHAHAHAHAH!

    Brain tumor.........I hate math.
     
  15. Ardens_Furore

    Ardens_Furore Jedi Padawan star 4

    Registered:
    May 14, 2001
    It might not have any imaginary roots. I think that there is a way to test for it, but I can't think of it right now. It's possible to have 5 of the same root (just like with some quadratics which have "double" roots where the discriminant is 0)

    I should qualify this with "That's what I think". I did this unit last year, but I seem to not have remembered a lot from it.
     
  16. neimoidian_85

    neimoidian_85 Jedi Padawan star 4

    Registered:
    Dec 30, 1999
    The best part of all this is that I'm a sophomore in the hardest class of math available for my grade and its still easy......
    WOW (SPACE BETWEEN WOW) COS, TAN, and SIN! Snooze.

    HAPPY! ;)
     
  17. Lobot_Omy

    Lobot_Omy Moderator Emeritus star 6 VIP - Former Mod/RSA

    Registered:
    Jul 9, 2001
    I don't recall WOW being part of my trigonometry class. 8-}
     
  18. Just_A_Slacker

    Just_A_Slacker Jedi Youngling star 4

    Registered:
    Aug 4, 2001
    I didn't say WOW a lot in my math classes. Mostly I just said "Son of a ..."
     
  19. Liz Skywalker

    Liz Skywalker Ex-Mod star 6 VIP - Former Mod/RSA

    Registered:
    Jun 13, 2000
    anyone???? [face_desperate]
     
  20. LoveisSuicideSP

    LoveisSuicideSP Jedi Padawan star 4

    Registered:
    Apr 23, 2001
    Hahahaha I'm only in Geometry. I have no clue what that problem means.
     
  21. Darth_Ignant

    Darth_Ignant Jedi Grand Master star 7

    Registered:
    Oct 24, 2001
    if x^5-81=0

    then x^5=81
    and

    x=5/81 (sorry can't draw it, but it's the square root sign with a 5 in the crook.)

    Havne't done real calc for 2 years and happily cannot really remember it :)

    actually, try this

    x^5-81=0

    =x^3x^2-9^2

    and then..um...I'll think of it..check in a few minutes
     
  22. Lt.Cmdr.Thrawn

    Lt.Cmdr.Thrawn Manager Emeritus star 6 VIP - Former Mod/RSA

    Registered:
    Sep 23, 1999
    x^5 - 81 = 0

    x^5 - 81 + 81 = 0 + 81

    x^5 = 81

    x = (the fifth root of) 81

    -------------------------------------------
    For those of you arguing about negative roots and stuff... how on earth did you get to that? This problem doesn't even involve i.

    -------------------------------------------
    Wait... 5 answers???

    I only got one! How odd.
     
  23. Kitt327

    Kitt327 Jedi Grand Master star 4

    Registered:
    Dec 23, 2000
    Who told you there were five answers, Liz? There is only one positive 5th root.
     
  24. legacyAccount

    legacyAccount Jedi Youngling

    Registered:
    May 22, 2012
    the obvious answer...

    42

    :p
     
  25. Jay

    Jay Jedi Grand Master star 5

    Registered:
    Dec 1, 1998
    x^5=81 is going to be an "s" curve with only one solution at 81.

    After you get to x^5 = 81, you take the 5th root of each side. You end up with a numerical value.
     
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