Adding a Trendline
A Trendline in Excel is a curve which attempts to "fit" a given set
of data. This is a common technique of mathematics. To find such a trendline
for a set of x and y coordinates, do the following:
- Enter the x and y data points side by side in two columns.
- Select the two columns and create an XY Scatter plot with Charts.
In this case, it is important that you select the first type
of sub-chart: data points only, and no curves connecting them.
Otherwise, you proceed as you normally would in graphing.
- When the graph is finished, it should consist of only points with no curves.
Select one of the points. This should select all of them. Then under the Chart menu
at the top of the screen, select "Add Trendline."
A dialog box will open with a column on the left with several choices.
- Choose "Type", you will select the type of function you
wish to use:
You will almost always want to choose a polynomial for the trendline. The
order of a polynomial is the highest degree, so an order 2 polynomial is a
quadratic, order three is a cubic, and so forth.
- We will generally want to know what the equation is that Excel came up with.
To see this, you choose "Options" from the list
Under "Options", you need to click the box for "Display equation
- Click OK and you're done. Below is an example of what a chart with a trendline
and displayed equation looks like:
- The equation (y=2.7044x^2+3.026x+1.9204) appears in the chart.
- The curve is an approximation to the data; it doesn't go through
all the data.
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