SLOPE OF A LINE
Slope of a line A line in a coordinate plane forms two angles with the x-axis , which are supplementary. The angle θ made by the line l with positive direction of x-axis and measured anti-clockwise is called the inclination of the line. Obviously 0° ≤ θ ≤ 180°. We observe that line parallel to x-axis, or coinciding with x-axis, have inclination of 0°. The inclination of a vertical line ( parallel to or coinciding with y-axis ) is 90°. If θ is the inclination of a line l, then tanθ is called the slope or gradient of the line l. The slope of a line having inclination 90° is not defined. The slope of a line is denoted by m. Thus m = tanθ, θ ≠ 90°. It may be observed that slope of x-axis is zero and slope of y-axis is not defined . Slope of a line when coordinates of any two points on the line are given Let P ( x, y ) and Q ( x, y ) be two points on a line l with inclination θ. Then slope is given by