The Slope of a Line
Example 1
Find the slope of the line that passes through the points (3, 2) and (3, 4).
Solution
Let (x_{1}, y_{1}) = (3, 2) and (x_{2}, y_{2})
= (3, .4). 
m 

Substitute these values in the slope formula. 


Simplify. 


Since division by zero is undefined, the slope is undefined. In fact, the slope of any vertical line is undefined. 
Slope of a Line
â€¢ Slope is positive: Line slants
upward as we move from left to
right.
â€¢ Slope is negative: Line slants
downward as we move from left
to right.
â€¢ Slope is zero: The slope of a
horizontal line is 0.
â€¢ Slope is undefined: The slope
of a vertical line is undefined. 

We can use slope to help us construct the graph of a line.
Example 2
Graph the line that passes through the point (5, 6) with slope
.
Solution
First, plot the given point, (5, 6).
To find another point on the line, use the slope. The slope,
, tells us how to move up and down (rise) and left and right (run) to get to
another point on the line. The slope
says to move 3 units
down and 4 units right to get to another point, (1, 3).
Plot the point (1, 3).
Finally, draw a line through the two points.
