Suppose a researcher plots a set of data for two variables on a coordinate plane and observes that the data are roughly linear. It may be useful to the researcher to have a linear formula relating x and y, but such a formula cannot be obtained by the alge- braic methods we have discussed in this section since the data are only approximately linear.Least-squares linear approximation of data is a procedure for finding a line posi- tioned so that the sum of squares of vertical distances from the data points to the line is minimized. The least-squares method is developed in Section 7.4. For now, you can use your calculator to find and apply the line that best fits a given set of data in the least-squares sense. This procedure is illustrated in Example 1.3.8.