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Math Help - rearranging exponential eq. help

  1. #1
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    rearranging exponential eq. help

    Hi Guys can anyone oint me in the right direction of making the exponetial part the subject. ie i need to solve for T

    (theta)=(Theta0) [1-e^-t/T}
    20 = 190x[1-e^40/T]


    im ok with transfroming eq's but not sure of the rules of this one


    any help appreciated
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  2. #2
    Junior Member
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    Is there a difference between "theta" and "Theta0"? I'm not sure what the first equation really is, it's confusing. I imagine that "Theta0" is the original theta value. I will solve for the second equation instead (by the way, is the time negative? -t = 40?)

     <br />
20 = 190x(1 - e^{\frac{40}{T}})<br />

    1 - \frac{20}{190x} = e^{\frac{40}{T}}

    ln(1 - \frac{20}{190x}) = \frac{40}{T}

     <br />
T = \frac{40}{ln(1 - \frac{20}{190x})}<br />

    Patrick
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  3. #3
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    Hi Patrick

    thanks for taking the time to reply

    That is spot on i did it another way working back over and got T = 360

    but couldnt work out how to set it out like you have

    Thankyou very much for your help
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