Formulae for Determining the Slope and Intercept

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Formulae for Determining the Slope and Intercept

To find the slope, calculate the deviation of each x from mean, , and calculate the deviation of each y from its mean, . The numerator is the product of the deviation of each x and y pair, the denominator is the sum of the squared deviations of all of the x-values. Thus the formula is:

The y-intercept, a, is calculated by substituting and into the equation of a line and solving for a:

To draw this line on a graph, substitute two or three values for x, calculate the corresponding y values, plot these x-y pairs as points on the graph, and draw a line through these points.