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Trigonometry
(thelemmy.club)
No memes, just stock photos
https://www.dailydot.com/unclick/youdontsurf-reddit-stock-photo-edit/
Carpenters won't be using it, because the tolerances for what they're doing are large enough not to matter, and they'll usually sneak up on a fit rather than spend time doing math.
As it happens it's not as important as it used to be, but knowing trig was at once point a necessary skill in skilled manufacturing roles.
This sort of thing:
Which today would be done with CNC, back in the day that guy needed to know how to calculate where each of those holes was going to be.
That particular image is a space shuttle part on a horizontal mill in the 1970s. I toured a shop at my local power utility doing very similar work on similar machines today. But they're not hiring kids out of school for that jobs, because fucking nobody knows trig anymore.