I’ve spoken about the many gaps in my mathematics education; I’ve written about a few. But in these cases, I was writing about the gaps at, say, the senior undergraduate to beginning graduate level.
I admit that I’ve enjoyed filling in some of these.
But, I also…have…elementary level gaps that I frequently overlook.
In my case: I never learned trigonometry all that well; I had forgotten about the laws of cosines and sines. And I had forgotten how to derive the following types of formulae: .
So, I spent a few minutes going over these old facts.
They aren’t hard but I am a bit surprised that I let my basic ignorance continue on this long.