Linest, trendlines and chart problem. Need help!
Posted by Corey Dale on February 13, 2002 3:43 PM
I have a quick question.
I have a set of 4 data points on a chart, with a 4th order polynomial trendline connecting the points. When plotted, the trendline looks like a bell curve.
I've used linest to give me the coefficients of the trendline equation, and then I used the Solver add-in to find the maximum y-value and the corresponding x- value.
My problem is this: When I choose to have the trendline equation shown on the chart, the 4th order trendline is only showing a 3rd order equation. I need to know if the values I get using LINEST are accurate, or if the trendline is not plotting correctly.
When I solve the equation, the numbers look good (they are which I'd expect to get), but the trendline doesn't plot right. In fact, the X and Y values I get using Solver don't even fall on the trendline as it is shown on the chart.
This is an example of the LINEST data I am using:
This gives me 5 coefficients for the equation.
Any ideas as to which might be wrong (calculated values or the way the trendline has plotted)?