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 Sep 18 answered Kuhn Tucker conditions, and the sign of the Lagrangian multiplier Sep 7 comment a problem with the induction hypothesis The inductive step is to show that whenever $p(n)$ is true, then $p(n+1)$ will also be true. Aug 31 comment Encyclopedia of Mathematics?(non-Alphabetical) This reminded me of a footnote by Sokal in his hoax article in Social Text (1996): "For a gentle introduction to set theory, see Bourbaki (1970)." Jul 15 comment Calculating the $k$th digit of $\pi$ The formula will also provide binary digits just as easily (since 4 binary digits = 1 hexadecimal digit). Jun 12 awarded Yearling Jun 3 comment Suppose $T$ is a linear operator $(V,V)$, and $T^2=T$. Does this means it is the identity operator? Operators with this property are in fact called projection operators. May 24 answered How to evaluate the determinant May 18 answered Can we still learn from the old masters? Feb 27 answered Necessary condition for positive-semidefiniteness — is it sufficient? Jan 29 answered Books / Articles on how mathematical education has changed over time Jan 26 revised mixed limit of ·$x^{-y}$ whenever x tends to $\infty$ and $y \to 0^{+}$ Removed unrelated tag Jan 26 revised How to define percentage values in terms of scalar values Removed unrelated tag Jan 24 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. Jan 24 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. Jan 19 answered Value of $\pi$ by Aryabhata Jan 13 answered geometry developments during the Islamic Golden Age (7-13 century) Dec 21 awarded Constituent Dec 9 awarded Caucus Dec 5 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." Nov 20 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.