9.6 Slope of a Line
As it is known any two given points contain a line. There can be various lines on a coordinate plane. Some of them parallel to the xaxis and some inclined to it. To answer the question  which way they incline and how much, is the concept of the slope of a line.
The slope of a line can be said to be the measurement of steepness of the line and its direction.
The line is said to have a positive slope if it rises from left to right as shown in the following figure 9.5 (a).
9.5(a)
9.5(b)
The line is said to have a negative slope if it rises from right to left (figure 9.5(b). The slope of a line is zero if it is parallel to the xaxis and it is undefined if it is parallel to the yaxis (see figure 9.6 (a) and (b)).
Slope : If a line passes through points A & B with
the coordinates ( x_{1}, y_{1}) & (x_{2},
y_{2}) then the slope of the line AB can be represented
as
If a line is parallel to the xaxis then its ycoordinate is the same for all the points on the line.
Therefore the slope of a line parallel to the xaxis is 0.
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