Wikipedia:Reference desk/Archives/Mathematics/2023 September 21

= September 21 =

Vocabulary Question
What exactly are the differences between the words "perpendicular", "normal", and "orthogonal"? I more or less use these words interchangeably, but I assume that they have precise definitions.  Puzzledvegetable Is it teatime already?  00:57, 21 September 2023 (UTC)


 * You can read perpendicular, Orthogonality, and Normal (geometry). They are pretty much the same, except that I think "normal" usually refers to vectors. Bubba73 You talkin' to me? 01:19, 21 September 2023 (UTC)
 * Perpendicular has to do with a string hanging straight down in the direction of gravity (perpendiculum = plumb line or plumb bob), typically at a right angle to the ground. Normal has to do with a right-angled stick (norma = carpenter's square). Orthogonal literally = right angled in Ancient Greek (came to English via French via Latin); the Latin analog is "rectangular". –jacobolus (t) 01:21, 21 September 2023 (UTC)
 * Each of these terms is used with several related but different meanings; the uses overlap, and which term is preferred in which context may be mostly a matter of tradition. One difference is that "normal" is often used as a noun (" the normal") and then refers to a one-dimensional object, while "orthogonal" is mainly used as an adjective and can apply to a pair of subspaces of a metric space that can have any dimensions. (Given an $m+n$-dimensional space, an $m$-dimensional subspace can be orthogonal to an $n$-dimensional subspace.) The geometric term "perpendicular" is mainly used in traditional Euclidean geometry. --Lambiam 17:21, 21 September 2023 (UTC)

Curious about UTC-Time zone
I am wondering who I can contact to know more about UTC -LOCK and whether its related to covid emergency broad cast related to ism band specific to geographic location.

Thanks Shireesh Avenger (talk) 03:03, 21 September 2023 (UTC)


 * I have no idea what "UTC-LOCK" refers to, but I am pretty confident it is not a mathematical topic. We have articles on UTC and Time zone. neither of which contains the word "LOCK". --Lambiam 17:05, 21 September 2023 (UTC)
 * A quick Google search for "UTC-LOCK" doesn't yield anything particularly useful. Rusty4321  talk contributions 23:56, 22 September 2023 (UTC)
 * Can you tell us something about the circumstances in which you came across the phrase "UTC -LOCK"? 88.111.190.170 (talk) 14:50, 29 September 2023 (UTC)