Equation for a Straight-line Relationship

Several methods can be used to develop an equation for a straight-line relationship, including (1) the graphical method, (2) the method of selected points, (3) the method of averages, and (4) the method of least squares. 

Graphical Method With the graphical method, the slope, m, and the y-intercept of the line are simply determined directly from the figure. The method involves two steps  

Step 2 For the slope, select two widely separated points and calculate the ratio of the difference in the ordinates and the difference in the abscissa values  

Method of Selected Points The following procedure is used for the method of selected points. Select two widely separated points. Substitute the coordinates 

Develop a straight-line equation using the method of selected points. 

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