Y Intercept

What’s the point?

Slope alone just gives you a direction, but that’s not enough. You need to have a starting point, or actually any point along the straight line to separate it from all the other lines going in the same direction but parallel to it. That starting point doesn’t change the slope of the line, it just moves it up or down.


  • Since any point will do to define exactly which line, why not pick an easy one to calculate?

    In an equation like:

    \mathbf{y}\ =\ \mathbf{m}\ \ast\ \mathbf{x}\ +\ \mathbf{b}

    if you set X to 0, it’s pretty easy to compute

  • Notice that the point on the X axis where X = 0 is, in fact, where the Y axis is. So… where the line you are plotting crosses the Y axis, it’s X value is 0, kind of by definition. 😉
  • Another word for “crosses” is “intercepts” and because the line of the function you’re plotting “crosses” or “intercepts” the Y axis where X = 0, the Y value at that “intercept” point is called the “Y Intercept”.
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