You can go ahead and use that equation, or you could figure it out every time, because if you know the total number of nodes, and you know the angular node number, then you know how many nodes you're going to have left.

你们可以直接用这个方程，或者每次都自己算出来，因为如果你们知道了总的节点数，又知道角向节点数，就知道剩下的节点数是多少。

麻省理工公开课 - 化学原理课程节选

And also that we know that the zero does not count as a node, if per se I actually had managed to hit zero in drawing that, so the correct answer would be the bottom one there.

另外你们要知道零点不是节点，假设说我确实把零点画成０了，那正确的结果就是底下这个。

麻省理工公开课 - 化学原理课程节选