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Math Help - Need logarithm work Checked

  1. #1
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    Need logarithm work Checked

    Hi. I just wanted to see if someone could check my work over. The only one im not so sure of is number 4 ( or bottom right) Thank you.
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  2. #2
    Member dokrbb's Avatar
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    Re: Need logarithm work Checked

    Quote Originally Posted by petenice View Post
    Hi. I just wanted to see if someone could check my work over. The only one im not so sure of is number 4 ( or bottom right) Thank you.
    concerning the last one - (a+b)^2 expands as a^2 + 2ab + b^2, but I'm not sure you have to go farther than the third step, though,

    dokrbb
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  3. #3
    MHF Contributor ebaines's Avatar
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    Re: Need logarithm work Checked

    You were fine up to

     \ln \frac {a-b}{(a+b)^2}

    But then with the next step you have  (a+b)^2 = a^2+ b^2, which is incorrect. If you multiply it out you get:

     (a+b)^2 = (a+b)(a+b) = a^2 + 2ab + b^2.

    In addition the step after that you go from  \frac {a+b}{a^2 + b^2} to  \frac {1 + b}{a + b^2}. This too is incorrect - if you were trying to divide both numerator and denominator by 'a' you would get  \frac {1 + b/a}{a+ b^2/a}.

    Also, although you didn't ask - you have an error in the first one: check the sign of the  \log_a z^2 term in the second line.
    Last edited by ebaines; April 22nd 2013 at 10:53 AM.
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  4. #4
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    Re: Need logarithm work Checked

    Ebaines - I actually meant for all of them to be checked so thank you for doing so. I think i have fixed the problem with number 4. Can you check again? I did it two different ways. I think they are both correct.

    Thank you.
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  5. #5
    MHF Contributor ebaines's Avatar
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    Re: Need logarithm work Checked

    That's better - good job!
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