**The Angle From the Horizontal - Rise Over Run**

When the slope of the line is 0, you know that the line is horizontal and you know it's a vertical line when the slope of a line is undefined.

n the Image, the subscripts on point A, B and C indicate the fact that there are three points on the line. The change in *y* whether up or down is divided by the change in *x* going to the right, this is the 'rise over run' concept

*y = mx* *+ b* is the equation that represents the line and the slope of the line with respect to the *x-*axis which is given by tan q = *m. *This is the slope-intercept form of the equation of a line. *(m for slope? Seems to be the standard!)*

When the slope passes through a point A(*x*1, y1) then *y*1 = *mx*1 + *b* or with subtraction *y - y1 = m (x - x1)*

You now have the slope-point form of the equation of a line.

You can also express the slope of a line with the coordinates of points on the line. For instance, in the above figure, A(x, y) and B(s, y) are on the line y= mx + b :

m = tan q = therefore, you can use the following for the equation of the line AB:

The equations of lines with slope 2 through the points would be:

For (-2,1) the equation would be: 2*x* - *y* + 5 = 0.

For (-1, -1) the equation would be: 2*x* - *y* + 1 = 0

The slope of a line can real life uses such as building stairs and ramps. The slope of a incline or decline is important in the construction of roads and important to ski racers and mountaineers.

See slope of a line.