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Math Help - Another log question

  1. #1
    Junior Member
    Joined
    Oct 2008
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    60

    Another log question

    Alright, I'm trying this problem and I am completely lost. Are there any websites to understand logs? I went to the tutorial in the helpful math sites section and after I got so far into, I was really lost.

    Anyways.. here's the question. Unlike the other one, I can't figure this out.

    All of these have the subscript of 2.
    log6-log15+log20.

    I tried first dividing the 6 by 15, and then multiplying the answer by 20 and ended up with 8. However, the answer in the back is 3, so I know I'm doing something wrong? I just don't get these things...
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  2. #2
    Super Member
    Joined
    Aug 2009
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    Israel
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    976
    Quote Originally Posted by Chinnie15 View Post
    Alright, I'm trying this problem and I am completely lost. Are there any websites to understand logs? I went to the tutorial in the helpful math sites section and after I got so far into, I was really lost.

    Anyways.. here's the question. Unlike the other one, I can't figure this out.

    All of these have the subscript of 2.
    log6-log15+log20.

    I tried first dividing the 6 by 15, and then multiplying the answer by 20 and ended up with 8. However, the answer in the back is 3, so I know I'm doing something wrong? I just don't get these things...
    Hi!

    log_2(6) - log_2(15) + log_2(20) = log_2(\frac{6}{15}20) = log_2(8)

    So far you were right. However, you only know so far that this expression is equal to log_2(8). Let's say x=log_2(8), then we need to find x!

    From the definition of logarithms,

    a^{log_a(n)} = n \Rightarrow 2^{log_2(8)} = 8 \Rightarrow log_2(8) = 3, since 2^3 = 8
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