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 Feb27 answered Necessary condition for positive-semidefiniteness — is it sufficient? Jan29 answered Books / Articles on how mathematical education has changed over time Jan26 revised mixed limit of ·$x^{-y}$ whenever x tends to $\infty$ and $y \to 0^{+}$ Removed unrelated tag Jan26 revised How to define percentage values in terms of scalar values Removed unrelated tag Jan24 comment length plus width equals price, factoring? You are using the same faktor $F$ in both cases. If $F$ is a constant then $P$ will be proportional to the perimeter of the rectangle. Jan24 comment Algebra on a Louvre tablet Geometric algebra would have been a correct tag (but not the tag geometric algebras, which dels with Clifford algebras!). The equation (2) above is essentially Euclid II.8. Jan19 answered Value of $\pi$ by Aryabhata Jan13 answered geometry developments during the Islamic Golden Age (7-13 century) Dec21 awarded Constituent Dec9 awarded Caucus Dec5 comment Does anyone know about Ramanujan's method of solving the quartic? The MacTutor History of Mathematics says that "Ramanujan was shown how to solve cubic equations in 1902 and he went on to find his own method to solve the quartic." Nov20 comment Show these sets are homeomorphic to eachother The notation $x\in \Bbb R^2\setminus \{0\}$ implies that $x=(x_1,x_2)$. Hence $x$ in jflipp's comments is really the same as $(x,y)$ in the question. Nov15 comment Why isn't Mary a victim of the permutation? You are really dividing by $1!4!4!$, since there are three groups of people to consider; Mary, female non-Marys, and male students. Nov5 answered Origin of the term `quermassintegral'. Oct2 comment Mathematical breakthroughs @AnalysisIncarnate I don't see any objective way to determine what is a breakthrough, and what is of less importance. Even if you say that only the creation of a new field of mathematics qualifies, most fields people work in today did not exist two centuries ago. Oct1 comment Mathematical breakthroughs This question is really too broad. A complete answer will include all major developments in all branches of mathematics during the last two centuries. Oct1 comment Geometry and land @ErelSegalHalevi The geometric problem would be to estimate the area of an irregularly shaped figure. Egyptian surveyors were called harpedonaptai, or rope stretchers, and presumably no angle measurements would be involved. Sep30 awarded Explainer Sep29 answered Geometry and land Sep17 answered Is the Riemann sphere homeomorphic to $\overline{\mathbb{R}}\times\overline{\mathbb{R}}$?