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 Apr15 comment How to estimate the axis of symmetry for an even function with error? You are welcome! If the large error is on the $y_i$'s, I've added a second (maybe more practical) method that could work. Apr15 revised How to estimate the axis of symmetry for an even function with error? added 671 characters in body Apr15 answered How to estimate the axis of symmetry for an even function with error? Apr8 awarded Enlightened Apr7 awarded Nice Answer Mar5 answered Show that $A =\left(\begin{smallmatrix}41&12\\12&34\end{smallmatrix}\right)$ is symmetric positive definite Mar4 comment Show that $A =\left(\begin{smallmatrix}41&12\\12&34\end{smallmatrix}\right)$ is symmetric positive definite Hint for alternative method: is there any relationship beetween $A$'s eigenvalues and quantities like, for example $\det A$? Jan31 accepted Differential of the inversion of Lie group Jan22 awarded Peer Pressure Jan22 comment Given $S \subset \Bbb{R}$, show $\textbf{int}(S)+\textbf{ext}(S)+\partial S =\Bbb{R}$ Hi @Kaytlyn, consider that some authors define $\partial S$ as the complement of $\text {int} S+\text {ext} S$ (for example Spivak in his book "Calculus on manifolds"). What's your definition of $\partial S$? Jan20 comment Does every differentiable ruled surfaces possess a global ruled parametrization? Hi @Evgeny, thanks for the suggestion. If I make some progress, I will post. Is there anything I can do to improve my question? Jan18 awarded Yearling Jan9 asked Does every differentiable ruled surfaces possess a global ruled parametrization? Dec9 awarded Caucus Nov27 asked Surjective $\gamma \colon I \to M^1$, $\gamma (t_1)=\gamma (t_2)$ can be extended to a periodic parametrization of $M^1$ Sep30 awarded Explainer Aug30 comment Alternative proof: Matrix $A$ is similar to $B$ iff $\lambda I - A$ is equivalent to $\lambda I - B$ I'm sorry, I've never heard this terminology. I assume it means $\exists P,Q\in GL(n,\mathbb K)$ such that $\forall \lambda \in \mathbb K$, $\lambda I - A=P^{-1}(\lambda I -B)Q$, right? Aug30 comment Alternative proof: Matrix $A$ is similar to $B$ iff $\lambda I - A$ is equivalent to $\lambda I - B$ I think that you should state the theorem more precisely: what values is $\lambda$ free to take? Since in this form it is obviously false: take $\lambda =0$. Aug30 comment Alternative proof: Matrix $A$ is similar to $B$ iff $\lambda I - A$ is equivalent to $\lambda I - B$ Matrix equivalence: en.wikipedia.org/wiki/Matrix_equivalence Aug29 comment The differential $\text d F_p$ is injective iff the pullback $F_p^*$ is surjective. Thank you anyway; as for your last remark, I was indeed trying to prove this using the canonical isomorphism $T_pM \simeq (m_p/m_p ^2)^*$, where $m_p$ is the ideal of germs that vanish in $p$. The differential identifies with the dual of the mapping $\varphi _p$ induced on $m_{F(p)}/m_{F(p)}^2$ by $F_p ^*$. In this case the problem is to prove that $\varphi _p$ surjective implies $F_p ^*$ surjective.