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Exponential formula problem

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    Exponential formula problem

    Hi,

    I have data plotted in a graph and an exponential trend function whose equation is y = 1E-07e53.122x.

    I'm trying to determine "y" from "x".
    The problem is when I try to enter the equation in excel. If I understand the equation well, "E" means 10 while e is 2.71... (EXP function). This would mean y = 1*10^(-7*EXP(53.122*x)).
    To this point, I don't know if I'm doing right because the results are non sense. The problem is that the value of the exponent for power 10 is really small. Can anyone explain me what I am doing wrong? I've checked other forums but I still stuck with it!

    The attachment is a simplified spreadsheet showing my problem. I'm looking for C, using B as X. The first graph on the right is the function curve, built using F2 to G11.

    Thanks and sorry for my so-so English! I hope the spreadsheet will open correctly as it has been built on a french computer. Link to file http://we.tl/sFqLLL66A4

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    Re: Exponential formula problem

    It would be

    = 0.0000001 * EXP(53.122 * x)

    However, you only have one significant digit for the coefficient. You should format the label to see more digits, or use a different method.
    Entia non sunt multiplicanda sine necessitate

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    Re: Exponential formula problem

    You are correct in your understanding between the distinction between scientific notation (E) and e (relating to the natural logarithm). However, your order of operations within your formula is incorrect.

    y = 1E-07e53.122x

    Think of 1E-07 solely as a constant. this would read 0.0000007

    Therefore, your formula should show a distinction between the coefficient and the use of the EXP() function.

    Something like this should work:
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    Where F11 is your corresponding x value. I believe your result is 0.0004, short of 0.0006, but that is why it is only a trendline of your data. Apply to F10 and F9, and you obtain values of 0.0002.

    Hope this helps!
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    Re: Exponential formula problem

    E means "exponential notation" -- essentially the computer version of the scientific notation you learned in school. It means mantissa * 10^exponent. Excel recognizes exponential notation, so there is not need to enter the 10 -- you can simply enter 1E-7 into a spreadsheet cell.

    So this formula (to the precision displayed) become 1E-7*exp(53.122*x). One thing to note: 1E-7 is only displayed to one significant figure. It is unlikely that this parameter is exactly 1.000000000E-7 -- it could be anywhere from 5E-8 to 1.5E-7 (an error range of about 50%). If you are going to use the values from the chart trendline regression, you will want to format the trendline to show all significant figures (to 15 digits).

    If this is something you will be doing regularly, I would suggest learning how to use the LINEST() or LOGEST() worksheet functions to perform these regressions. https://support.office.com/en-us/art...rs=en-US&ad=US
    Quote Originally Posted by shg
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    Re: Exponential formula problem

    Thanks everyone! I have changed the equation to 1E-7*exp(53.122*x) and it works like a charm. Also, I will explore LINEST and LOGEST in a near future!

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