How do you extend (or CAN you extend) the static Math methods?

Answer 1

Extension methods are a way to make your static methods appear to be instance methods on the type they "extend". In other words you need an instance of something in order to use the extension method feature.

It sound to me that you're going about it in the opposite way by trying to make Math.Cos handle your type. In that case, I'm afraid you have to implement the functionality yourself. If that is not what you're trying to do, please clarify.