In this video the instructor shows how to derive a general equation for a line in Point-Slope form. The slope of an equation is the ratio of difference of y coordinates to the difference of x coordinates. In other words, slope is the change of y up on change of x. So you have the basic slope equation m = (y2 - y1)/(x2 - x1). When you have fractions you can simplify them by multiplying the denominator to the numerator on both sides. So multiply the equation by (x2-x1) on both sides. This gives you m(x2 - x1) = (y2 - y1). This is the general form of a line in point slope form. So the general equation can be also written as (y - y1) = m(x - x1). This video shows you how to write an equation of line in Point-Slope form.