The equation of a straight line is usually written in the
y = mx + c, where the number c gives the values of the y-coordinate
where the line crosses the y-axis and the number m is the
gradient or slope of the line.
of the line m at one point P1 = (x1, y1) through which the
line passes, can be calculatoed by equation (y - y1 ) / (x
- x1) = m