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Math Help - exponential function

  1. #1
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    exponential function

    I am having trouble solving with the following problem:

    If 15^2x=4, what does 15^2x equal

    How do you rewrite 15^2x=4 so x can be solved for without a calculator?

    Any help is appreciated
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  2. #2
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    Re: exponential function

    Hey phasediagram.

    Hint: 15^2x = (15^2)^x = 225^x = 4. Do you know about logarithms?
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  3. #3
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    Re: exponential function

    I am learning about logarithms now. i seem to be drawing a blank
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  4. #4
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    Re: exponential function

    With logarithms if a^x = y then log_a(y) = x where log_a is the logarithm to the base a. The common bases are the natural base e and base 10. To get any base you use the formula log_a(x) = log_b(x)/log_b(a) where log_b is the logarithm in base b and you use b = e (natural) or b = 10 where a is any base that is a whole number typically greater than 1 (but it can be in between 0 and 1 not including those two numbers).
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  5. #5
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    Re: exponential function

    got it! thanks
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  6. #6
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    Re: exponential function

    You can also proceed directly by taking log on both sides and you will get 2x log 15 = log 4
    x = (1/2) [ (log 4 )/ ( log 15)] Now just plug in values of log and you will get the value of x
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