http://www.bing.com:80/search?q=Un+Useable+CodeSearch resultshttp://www.bing.com:80/s/a/rsslogo.gifhttp://www.bing.com:80/search?q=Un+Useable+CodeCopyright © 2026 Microsoft. All rights reserved. These XML results may not be used, reproduced or transmitted in any manner or for any purpose other than rendering Bing results within an RSS aggregator for your personal, non-commercial use. Any other use of these results requires express written permission from Microsoft Corporation. By accessing this web page or using these results in any manner whatsoever, you agree to be bound by the foregoing restrictions.https://math.stackexchange.com/questionsMathematics Stack Exchange is a platform for asking and answering questions on mathematics at all levels.Sun, 12 Apr 2026 08:11:00 GMThttps://math.stackexchange.com/questions/153902/un-countable-union-of-open-setsA remark: regardless of whether it is true that an infinite union or intersection of open sets is open, when you have a property that holds for every finite collection of sets (in this case, the union or intersection of any finite collection of open sets is open) the validity of the property for an infinite collection doesn't follow from that. In other words, induction helps you prove a ...Tue, 14 Apr 2026 19:50:00 GMThttps://math.stackexchange.com/questions/1426699/double-induction-example-1-q-q2-q3-cdots-qn-1-qn-fracSlightly relevant: you can see my answer on this thread for a proof that uses double induction (just to get you exposed to how the mechanics of a proof using double induction might work).Tue, 14 Apr 2026 02:11:00 GMThttps://math.stackexchange.com/questions/276644/prove-that-that-un-is-an-abelian-groupProve that that $U(n)$, which is the set of all numbers relatively prime to $n$ that are greater than or equal to one or less than or equal to $n-1$ is an Abelian ...Wed, 08 Apr 2026 21:59:00 GMThttps://math.stackexchange.com/questions/1777280/the-sequence-of-integers-1-11-111-1111-ldots-have-two-elements-whose-diffProve that the sequence $\ {1, 11, 111, 1111, .\ldots\}$ will contain two numbers whose difference is a multiple of $2017$. I have been computing some of the immediate multiples of $2017$ to see howSat, 11 Apr 2026 15:22:00 GMThttps://math.stackexchange.com/questions/314846/for-what-n-is-u-n-cyclicWhen can we say a multiplicative group of integers modulo $n$, i.e., $U_n$ is cyclic? $$U_n=\ {a \in\mathbb Z_n \mid \gcd (a,n)=1 \}$$ I searched the internet but did ...Sun, 12 Apr 2026 12:22:00 GMThttps://math.stackexchange.com/questions/2207334/como-calcular-el-area-de-la-superficie-de-un-huevo-con-calculo?noredirect=1&lq=1Estoy haciendo mi reciente evaluación interna del IB Matemáticas HL y mi tema es cómo calcular el área de superficie de un huevo . Quiero aplicar el cálculo conocimiento en esta pregunta, pero mi conocimiento sobre esta área es limitada.Mon, 13 Apr 2026 09:22:00 GMThttps://math.stackexchange.com/questions/3164783/prove-that-the-sequence-11-nn-is-convergentI know the proof using binomial expansion and then by monotone convergence theorem. But i want to collect some other proofs without using the binomial expansion. *if you could provide the answer w...Sat, 11 Apr 2026 21:20:00 GMThttps://math.stackexchange.com/questions/1351058/circle-revolutions-rolling-around-another-circleAt the risk of sounding very un-mathematical, how do the (infinite set of) points on the circumference of each circle map to each other to accomplish this? Consider Circle A rolling along a straight line the length of the circumference of Circle B. Then it will revolve 3 times.Tue, 31 Mar 2026 07:35:00 GMThttps://math.stackexchange.com/questions/2993418/mnemonic-for-integration-by-parts-formulaThe Integration by Parts formula may be stated as: $$\\int uv' = uv - \\int u'v.$$ I wonder if anyone has a clever mnemonic for the above formula. What I often do is to derive it from the Product R...Sat, 11 Apr 2026 16:33:00 GMT