Straight Lines

Slope of a line: If θ is the inclination of a line l (the angle between positive x-axis and line l), then m = tan θ is called the slope or gradient of line l.

The slope of a line whose inclination is 90º is not defined. Hence, the slope of the vertical line, y-axis is undefined. The slope of the horizontal line, x-axis is zero.

For example, the slope of a line making an angle of 135° with the positive direction of x-axis is m = tan 135° = tan (180° – 45°) = – tan45° = –1

Slope of line passing through two given points:

The slope (m) of a non-vertical line passing through the points (x1, y1) and (x2, y2) is given by…

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