A window washer is 100 feet high on a building. He begins to lower his scaffold at a rate of 10 feet per second. The grid shows his building height after a given time in seconds.

     

As you notice, the rate of decrease is constant. Each second, the window washer is lowered 10 feet. After one second, the window washer is at 90 ft. After two seconds, the window washer is at 80 feet. After three seconds, the window washer is at 70 feet etc. This relationship can be shown as: The rate of change is (-10 feet)/(1 second).

The slope of the line is the ratio of the number of units the line rises or falls vertically (the rise) to the number of units the line moves horizontally from left to right (the run).

Try finding the slope on your own. 1) Find the slope of the line containing the points (3,1) (4,5) and 2) Find the slope of the line containing the points (-3,1) (-2,-3). When you are finished check your answer below. Follow the instructions to calculate the answer.

The slope of a horizontal line equals zero.

The slope of a vertical line is undefined since division by zero is undefined.

Try finding the slope of the line containing the given points. A) (-1,2) and (2,2)   B) (3,2) and (3,5). After you have worked them out, plot the points on the slope generator above to check your answers.

Note:

A line with a positive slope (ie. 2, 3/4, 25), passes through the 1st and 3rd quadrant. A line with a negative slope (ie. -3, -.5, -30), passes through the 2nd and 4th quadrant.