Area under trendline

J

Josh

Does anybody know how to find the area under the curve of a trendline (6th
degree polynomial in my case).

Thanks in advance for any help.
 
J

Jerry W. Lewis

There is no native Excel function for integration, but integrating a
polynomial is straightforward. Assume the coefficients are in A2:G2 (as in
output of LINEST for fitting a polynomial) and the corresponding powers are
in A1:G1. The value of the polynomial at x is then
=SUMPRODUCT(A2:G2,x^A1:G1), and the integral from a to b of the polynomial is
=SUMPRODUCT(A2:G2/(A1:G1+1),b^(A1:G1+1))-SUMPRODUCT(A2:G2/(A1:G1+1),a^(A1:G1+1))

Jerry
 

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