Question 101525
The slope of a line through two given points is defined by the equation:
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slope = (change in y)/(change in x)
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You were given that point 1 is (-5, -4) and point 2 is (3, -4)
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In going from point 1 to point 2 the value of x goes from -5 to +3.  On the number line that
requires a change of +8 units. If we plug this into the slope equation, we get:
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slope = (change in y)/8
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What is the corresponding change in y from point 1 to point 2? Notice that in point 1 the
value of y is -4 and when you go to point 2 the value of y is also -4. Since these are the 
same there is zero change. When you substitute this change in y into the slope equation it 
becomes:
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slope = 0/8
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and zero divided by 8 is zero. So the slope is zero.  What does this mean? It means that
the line is a horizontal line because it has no slope up or down.
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You can convince yourself of this by plotting the two given points on a graph and then
drawing a line connecting the two points. You should see that it is a horizontal line ...
which means "no slope" or "zero slope."  
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Hope this helps you to understand the problem.  As you get more familiar with this concept
you will just be able to look at a similar set of points and recognize that if there
is a change in x values of two points, but no change in the y values of the two points, the
slope is zero.
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