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
No that's wrong.
But I need to find the slope, which requires 2 points (y2-y1 over x2-x1).
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)\
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
y2 - y1
m = ---------
x2 - x1
where (x1,y1) = (0,0) and (x2,y2) = (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