Video narration
Why can one straight line have several different equations? Think of a ramp you've walked on: its steepness depends on how much it rises for the horizontal distance you travel. A line's slope works the same way. It is the change in y divided by the change in x; a vertical line has no defined slope. If you know a line's slope and where it crosses the y-axis, slope-intercept form shows both directly. If you know the slope and one point on the line, point-slope form uses that information. And if you know two points, two-point form describes the line from those coordinates. The line stays the same; only the information you start with changes. So, slope is how much y changes per unit of x, and several equations simply reflect what you know first.