k=(y1-y2)/(x1-x2)。
The slope known as "angle coefficient", represents the amount of inclination of a straight line on a plane at right angles to the axis of abscissa represents coordinates.
Linear tgα tangent of the inclination angle α of the X-axis is referred to as "slope" of the straight line, and denoted by k, k = tanα. A predetermined straight line parallel to the X axis of the slope is zero, the Y-axis is parallel to the slope of the line does not exist. For over two known points (x1, y1) and a straight line (x2, y2), if x1 ≠ x2, the slope of the line is k = (y1-y2) / (x1-x2)