On Wed, 22 Oct 2008 10:21:02 -0700, Oligo wrote:

hi,
if i have 2 column of data like
A B
100 10
200 36
300 45
400 60

how can i get the b values for input of values that are in between my column
A data? im currently ploting out the graph and using the trendline eqn to
obtain my results.however polynomial power6 curve still cannot approach my
table data well.
wonder if i can do some what-if-analysis to interpolate the 2 column?

Given the data you present above, a 3rd order polynomial as an R^2 of 1. Can't
get too much better fit than that.

If your "real" data doesn't match the data you've presented, you'll have to
make some decision as to how you will interpolate between points.

One common problem in trying to apply the formula on a graph to real data is
the precision of the values displayed. If that is what you are trying to do,
and is your problem, right-click on the formula, then select "format trendline
label". Format the number to 15 decimals and use those values.

Or, you could use the LINEST equation. To use the LINEST equation to predict
the B value given a new A, using the 3rd order polynomial:

=SUMPRODUCT(X^{3,2,1,0},LINEST(B,A^{1,2,3}))

where X is your unknown A.

--ron