.. Copyright (C)  Google, Runestone Interactive LLC
   This work is licensed under the Creative Commons Attribution-ShareAlike 4.0
   International License. To view a copy of this license, visit
   http://creativecommons.org/licenses/by-sa/4.0/.

.. _creating_line_of_best_fit:

Creating a Line of Best Fit
===========================

In order to analyze a line of best fit for a scatter plot, you will first need
to make one. You can do this in Sheets through an option in the chart editor.
After making a scatter plot, you can add a line of best fit by opening the chart
editor by clicking the three dots in the top right corner.


.. image:: figures/edit_chart.png
   :align: center
   :alt: Screenshot showing how to edit a chart by clicking the three dots in the top right corner.

Once the chart editor is open, make sure customize is selected. Under “Series”,
there is a checkbox to add a trendline. You can change the color and thickness
of the line, display the :math:`R^{2}` value, (this is the same as the
coefficient of determination), and display the equation of the line.


.. image:: figures/add_trendline.png
   :align: center
   :alt: Screenshot showing how to add trendline.

Once you have added a trendline, it will appear on your graph.


.. image:: figures/average_sat_score_completion_rate.png
   :align: center
   :alt: Scatter plot with a trendline.


Now that there is a trendline and equation of a line on the graph, you can use
this information to analyze data and predict results given your data. In
particular you can use the slope and y-intercept. Don't worry if you don't
remember how to find this information from the equation of a line, the next
section will guide you through this.