A line of best fit is a line chosen to summarize the relationship between two numerical variables. Under the ordinary least
squares criterion, the fitted line 
minimizes the residual sum of squares
 |
(1)
|
When the 
are not all equal, the minimizing coefficients are
 |  |  |
(2)
|
 |  |  |
(3)
|
Other definitions of best fit arise from different loss functions or assumptions about residuals in both coordinates.
