Why does the video square the $x - \bar{x}$ column when preparing the slope formula?

The final fitted regression equation is $\hat{y} = 2.2 + 0.6x$. This is assembled by substituting the computed intercept $b_0 = 2.2$ and the computed slope $b_1 = 0.6$ into the general linear model $\hat{y} = b_0 + b_1x$.

Conditions: The data set consists of the five specific points (1,2), (2,4), (3,5), (4,4), and (5,5).; The slope $b_1$ has been calculated as 0.6.; The intercept $b_0$ has been calculated as 2.2.

The slope $b_1$ is computed by dividing the sum of the cross-products of deviations by the sum of the squared x-deviations. In the worked example, the sum of the cross-products is 6 and the sum of the squared x-deviations is 10, yielding $b_1 = 6/10 = 0.6$.

Conditions: The data set consists of paired observations.; The sample means $\bar{x}$ and $\bar{y}$ have been computed.; The denominator $\sum (x_i-\bar{x})^2$ is nonzero.

The y-deviations are calculated by subtracting the sample mean of the y-values, $\bar{y}=4$, from each individual y observation in the table. This produces a column of signed deviations measuring how far each point lies above or below the horizontal mean line.

Conditions: The y-values in the table are 2, 4, 5, 4, and 5.; The sample mean $\bar{y}$ has been computed as 4.

The intercept $b_0$ is calculated by substituting the mean point $(\bar{x}, \bar{y})$ and the known slope $b_1$ into the regression equation $\hat{y} = b_0 + b_1x$, and then solving algebraically for $b_0$. In the example, substituting $x=3$, $\hat{y}=4$, and $b_1=0.6$ yields $4 = b_0 + 0.6(3)$, which simplifies to $b_0 = 2.2$.

Conditions: The slope $b_1$ has already been computed.; The sample means $\bar{x}$ and $\bar{y}$ are known.; The regression line is assumed to pass through $(\bar{x}, \bar{y})$.

The column $(x - \bar{x})(y - \bar{y})$ represents the product of the x-deviation and the y-deviation for each observation. It is used to build the numerator of the least-squares slope formula, capturing how x and y vary together relative to their means.

Conditions: The x-deviations and y-deviations have been computed for each row.; The data set consists of paired observations.