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Math Wizards

Discussion in 'Off-topic Zone' started by Joshmil53, Oct 31, 2012.

  1. Joshmil53

    Joshmil53 Active Member

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    Just got done taking a test in my Alg class. I had trouble with one problem though.

    2^(x+1)=5^(3x)

    My answer came out to line -.66 when solved and he said to leave it in logarithmic form. My answer was something like x =((ln5/ln2)-1)/-2. I looked through my notes and everything and couldn't find a problem like it, can someone help me?
  2. Phoenix

    Phoenix Well-Known Member

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    42.....?
  3. Joshmil53

    Joshmil53 Active Member

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    I thought someone might say that lol
  4. Phoenix

    Phoenix Well-Known Member

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    :laugh2::D
  5. Joshmil53

    Joshmil53 Active Member

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    Why can't I edit threads after so long? A mod can delete/lock this please.
  6. theogt

    theogt Surrealist Zone Supporter

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    Slightly embarrassed I don't remember how to solve this.
  7. dexternjack

    dexternjack World Traveler Zone Supporter

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    take logs of both sides..
    (x+1)log2 = (3x)log 5
    x+1 = 3x log5/log2
    x+1 = (3x)(2.3219)
    x+1 = 6.9658x
    5.9658x = 1
    x = 1 / 5.9658 = 0.1676
  8. Joshmil53

    Joshmil53 Active Member

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    That's much clearer -ln2/(ln2-3ln5). I can't believe I messed something up so easy lol. Oh well, should get some credit.
  9. Diogenes

    Diogenes Active Member

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    Too bad this was a math problem. Had it been an essay or thesis, all you would have needed to do was post it anywhere in the forum and the grammar and spelling police would have went over it with a fine tooth comb, essentially editing it for free.
  10. Yeagermeister

    Yeagermeister Active Member

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    :laugh1:
  11. Phoenix

    Phoenix Well-Known Member

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    If you say so. :write::eek:hno::huh::):eek::
  12. bigdnlaca

    bigdnlaca Active Member

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    Well I knew that it was higher than 0 but less than 1.
  13. SaltwaterServr

    SaltwaterServr Blank Paper Offends Me

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    Do yourself a HUGE favor and get a TI-89 Platinum if you're allowed to use it in class.
  14. Joshmil53

    Joshmil53 Active Member

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    I goy a ti-83plus because it was free through the school (16 in college, my high school pays for everything). What's a ti-89 do?
  15. dexternjack

    dexternjack World Traveler Zone Supporter

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    I hurried through mine w/o thinking all the way. I have a minor in Math so I tend to over-think it and solve too fast. I made a minor error in translating, here it is...

    2^(x+1) = 5^(3x)
    log2^(x+1) = log 5^(3x)
    (x+1)log 2 = (3x)log 5
    xlog2 + log2 = 3xlog5
    xlog2 - 3xlog5 = -log2
    x(log2 - 3log5) = -log2

    x = -log2 / (log2 - 3log5) -this is the form your teacher was asking for...

    if you were to solve for x, then you would get .167

    It has been a very long time since I have done these, but I am pretty confident this is correct.
  16. Joshmil53

    Joshmil53 Active Member

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    It is.

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