A way of understanding your question is that someone has given you a spreadsheet with a graph on which there is a linear trendline with the equation of the trendline displayed. Select the trendline formula in the chart. If you want your chart to make you look smart scroll down in the Format Trendline menu and check Display Equation on chart and Display R-squared value on chart.
Check the box labeled Display Equation on Chart and then close the window.
Youll see something like whats in the red box below appear on your chart. A trendline also called a line of best fit is an analytical tool that is used to visualize and represent the behavior of a data set to see if theres a pattern. Check the box labeled Display Equation on Chart and then close the window. Where b1 b6 and a are constants.