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Math Help - Logarithm Help

  1. #1
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    Logarithm Help



    A, B, and D worked out, but when I try to do C I run into a problem.

    I use the formula:
    f(t)=90-15log(6+1)

    For an answer I get:
    90+log(1/474561509943)

    Im pretty sure im doing something wrong because the other answers were more like 90 and 50
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  2. #2
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by whiteforlife View Post


    A, B, and D worked out, but when I try to do C I run into a problem.

    I use the formula:
    f(t)=90-15log(6+1)

    For an answer I get:
    90+log(1/474561509943)

    Im pretty sure im doing something wrong because the other answers were more like 90 and 50
    When I did 90-15log(7) I got an answer of 77.3 (3sf). Are you sure you put it in your calculator correctly?

    Google's calculation
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  3. #3
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    That was it. I did it in my calculator wrong 3 times. Thanks for catching my stupid mistake. Also for part E, would about 6 months be a correct answer or is it supposed to be exact?
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  4. #4
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by whiteforlife View Post
    That was it. I did it in my calculator wrong 3 times. Thanks for catching my stupid mistake. Also for part E, would about 6 months be a correct answer or is it supposed to be exact?
    I got an answer of 9 (I assume t is in months)

    75 = 90 - 15log_{10}(t+1)

    75-90 = -15log_{10}(t+1)

    -15 = -15log_{10}(t+1)

    -15 will cancel to give us log_{10}(t+1) = 1

    t+1 = 10^1 = 10

    t=9
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