Pythagorean Addition (opens in new tab)

TL;DR: Instead of labouriously computing \(c = \sqrt{a^2 + b^2}\), we can mentally calculate using the alpha-max plus beta-min algorithm, by estimating \[\hat{c} = \mathrm{max}\left(a, 0.9a + 0.5b \right)\] and this will be very close to the actual \(c\). This is useful for adding up sources of variance, or figuring out radiuses, or other such things. (Continue reading the full article on the web.)