Question 717845
y2 - y1
-------- = slope  {"rise over run"}
x2 - x1


(1,-9) and (4,-9) are the coordinates (x1,y1) and (x2,y2)


-9 - (-9)
---------- = slope {substituted coordinates into slope formula}
4 - 1


-9 + 9
------- = slope {simplified the numerator}
3


0
-- = slope {added in the numerator}
3


= 0   {divided}


slope is 0
A line with a slope of zero has no "rise",
it is a horizontal line


Also, once you notice the y-coordinates are the same, you can determine it is a horizontal line.   If the x-coordinates are the same, it is a vertical line.  If it is a positive, slope the line slants up and to the right.  If it is a negative slope, the line slants down and to the right.
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