Relating to or being an extreme value; in mathematics, describing a function or path that maximizes or minimizes some quantity.
From extremum + -al (adjective suffix). A technical mathematical term that became formalized in calculus and optimization theory during the 19th-20th centuries.
In physics, the path light takes is always extremal—it maximizes or minimizes time—which is so profound that even light seems to 'choose' the best route, though it's really just following the rules of nature!
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