A best fit line is a straight line that most closely represents the relationship between a set of data points. It is used to predict future values or to understand the trend of the data. In Excel, you can use the LINEST function to find the best fit line for a set of data.
The LINEST function takes three arguments: the y-values, the x-values, and a constant value. The y-values are the values that you want to predict, and the x-values are the values that you know. The constant value is a logical value that specifies whether or not the intercept of the line should be forced to zero.