I thought about trigonometry today. (No, really, I did!)
For some reason, for the first time in about 50 years, I remembered trigonometry. It was one of the triumvirate of high school math courses everybody in a "college-bound" curriculum had to have: geometry, trigonometry, algebra. I also took a college-credit course (which would now be known as "advanced placement), in calculus.
Of those four courses I have found some use in life for geometry, algebra, and even calculus, which is central to probability theory. But I can't think of a single instance where I've ever had to concern myself with the secants, tangents, and sines that are the bread-and-butter of trig. I've never even cosined a loan! Nor could I recall, when I thought about it, exactly what trigonometry was about.
Wikipedia to the rescue! Trigonometry "studies triangles and the relationships between their sides and the angles between these sides." Gee, that makes it clearer, doesn't it? What was most shocking was that the subject is said to be a prerequisite for calculus. As I said, I took calculus, I passed calculus, and I remember a major focus on measuring the space under a wavy line ... but I don't recall trigonometry being involved in it.
I suppose it's a good thing I didn't go into certain fields like astronomy and navigation, where trig is said to be essential. Since I didn't, though, I'm free to again forget all about trigonometry, the one subject in high school that seems to have been a total waste.