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9.6 Slope of a Line
As it is known any two given points contain a line. There can be various lines on a co-ordinate plane. Some of them parallel to the x-axis 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 x-axis and it is undefined if it is parallel to the y-axis (see figure 9.6 (a) and (b)).
Slope : If a line passes through points A & B with
the co-ordinates ( x1, y1) & (x2,
y2) then the slope of the line AB can be represented
as
If a line is parallel to the x-axis then its y-co-ordinate is the same for all the points on the line.
Therefore the slope of a line parallel to the x-axis is 0.
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