need help entering trendline formula

  • Thread starter Thread starter Jim
  • Start date Start date
J

Jim

I need help to enter the following formula into a cell:

y=21.155e ^-0.006x

This is the formula of a trendline from a graph of only 5 points, and I
would like to enter this formula into a column of cells for the purpose of
predicting future values of y. The value of x has a range of 0 to 165, and
is located in a colum starting at A4

R squared = .9928 in this case

I usually can figure out this sort of thing in Excel, even if it takes a
while, but this one has me stumped. In this case Excel does not want to
accept this formula

Thanks
Jim
 
y=21.155e ^-0.006x

Hi. Excel can not do implied multiplication.
Here is one way, where cell A1 is your 'x' variable.

=21.155*EXP(-0.006*A1)

HTH
Dana DeLouis
 
Jim said:
I need help to enter the following formula into a cell:
y=21.155e ^-0.006x
Click to expand...

In that formula, "e" is the transcendental "e", not to be confused with the
scientific notation "E+00". And "x" is the value of x. For example, for
the first data point:

=21.155*exp(1)^(-0.006*A4)

which is better written as:

=21.155*exp(-0.006*A4)

FYI, 0.006 is probably a poor estimation. You can increase the precision by
pointing to the formula in the chart and doing: right-click, click Format
Data Labels > Number, and select a number format with an appropriate number
of decimal places.

Alternatively, you can compute the "exact" coefficient for the formula
a*exp(b*x) as follows:

a: =exp(index(linest(ln(B4:B8),A4:A8),1,2))

b: =index(linest(ln(B4:B8),A4:A8),1)

That assumes that "x" values are in A4:A8 and corresponding "y" values are
in B4:B8.


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