In order to describe a straight line, the or is used, but if you know the line's (slope) and an point on the line, you can use the point-slope formula.
By using the known coordinates and in the point-slope form, you can rearrange for and get the slope-intercept form, .
The point-slope equation is just a rearranged version of the form used to calculate the line's (slope).
The specific point
is then replaced by the more general
, which then gives us the point-intercept form.