## Wiskomen Hi everyone, since two days I'm following the lesson 18.01SC and I don't really understand this: In Session 2, Clip 2 he explaines that to get the x-intercept of the triangle you have to use this formula: y - y0 = m (x - x0) with: y = 0, because it is an intercept with the x-axes. y0 = 1/x0 m = -1/x0^2 x = x x0 = x0 But I don't get why it is y - y0 and not just y0 and why it is m (x - x0)... Could someone please help me with this? If it is a bit of a stupid question, I'm sorry. one year ago one year ago

Let's start by looking at the formula in question. M represents slope, which is defined by the rate of change of y divided by the rate of change of x, or rise over run. Since rate of change requires change over some period, you need two points: an initial point (x0 or y0), and a change point (x or y). From the definition and the statement above you get the equation $m = \frac{ (y - y0) }{ (x - x0) }$ Multiplying both sides of the equation by (x - x0) yields the formula you are referring to, $y-y0 = m(x-x0)$ , Which as you see follows from the original statement. Do you understand now?