Question 51250
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Driving down a mountain, Tom finds that he has descended 1800 ft
in elevation by the time he is 3.25 mi horizontally away from 
the top of the mountain. Find the slope of his descent to the 
nearest hundredth. I thought that the first step would be to 
create an equation

y= 3.25x + 1800
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No that's wrong.
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But I need to find the slope, which requires 2 points (y<sub>2</sub>-y<sub>1</sub> over x<sub>2</sub>-x<sub>1</sub>). 
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OK, we can do it using that formula.

Let's put him at the origin (0,0).  Then the top of the mountain
is 3.25 miles or 3.25×5290 ft or 17160 feet to the right of the origin
and 1800 feet up. This means the top of the mountain is at the point
(17160, 1800).
                                      (17160,1800)   
 (0,0)\{{{ graph(350, 65, -1000, 20000, -1000, 3000, 1800x/17160) }}}
       
He is at the origin (0,0) and the top of the mountain (17160, 1800) is
at the upper right corner of the above graph.

So let's use the formula for slope

     y<sub>2</sub> - y<sub>1</sub>     
m = ---------
     x<sub>2</sub> - x<sub>1</sub>

where (x<sub>1</sub>,y<sub>1</sub>) = (0,0) and (x<sub>2</sub>,y<sub>2</sub>) = (17160. 1800)

      1900 - 0       1800      15
m = ----------- =  ------- = ----- = .1 approximately 
     17160 - 0      17160     143

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Note: We could have just used the fact that slope means
"rise over run" where the rise is 1800 feet and the
run is 3.25 miles or 17160 feet. Then

slope = rise/run = 1800/17160 = 15/143 = .1 approximately

Edwin</pre>