Honors Geometry Companion Book, Volume 1

3.2.1 Finding the Slope Given Two Points (continued)

Example 3 In Example 3, the slope of a line is found by using the slope formula when a graph of a line is given, and then the meaning of the slope is explained in the context of the situation.

Consider this example. Find the slope by substituting the coordinates from the points (12, 1200) and (24, 600) into the slope formula. Remember, slope is the ratio of the change in y to the change in x . Here, the variable y represents the value of the computer in dollars, so “change in y ” can be translated as “change in value”. The variable x represents the time (in months) that has passed since the computer was purchased, so “change in x ” can be translated as “change in time”. The slope was found to be − 50, or − 50/1. The negative indicates a decrease, 50 is the change in value , and 1 is the change in time . Therefore, a slope of − 50 means that the value of the computer decreases by $50 each month.


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