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Ask HN: What are some neat or useful equations you know?
3 points by y33t 439 days ago
Something worth saving in a programmable calculator, like Naismith's Rule [1] or calculating the day of week for any date [2].

1: https://en.wikipedia.org/wiki/Naismith%27s_rule

2: https://cs.uwaterloo.ca/~alopez-o/math-faq/node73.html