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 Dec17 accepted How does the triangle inequality work for $|x-y|$? Dec17 comment How does the triangle inequality work for $|x-y|$? Nevermind - I found a proof that shows the inequality using $|x+y|$ Dec17 comment How does the triangle inequality work for $|x-y|$? But my question, though, is how $||x|-|y||\leq|x+y|$? My textbook says (without proving) that $||x|-|y||\leq|x+y|\leq |x|+|y|$. Dec17 comment How does the triangle inequality work for $|x-y|$? I have here that $||x|-|y||\leq|x+y|\leq |x|+|y|$... I was able to find several proofs of the "reverse triangle inequality", but they all start off with $|x-y|$ instead of $|x+y|$ like in the upper and lower bounds given. How does this proof translate from $|x|-|y|\leq |x-y|$ to $||x|-|y||\leq |x+y|$? Dec17 asked How does the triangle inequality work for $|x-y|$? Nov25 awarded Popular Question Nov6 asked How to conclusively determine the interior of a set Nov5 awarded Nice Question Nov4 asked Convert a WFF to Clausal Form Nov4 accepted Finding the matrix of a linear transformation relative to two non-standard bases Nov3 comment Finding the matrix of a linear transformation relative to two non-standard bases @Omnomnomnom Unfortunately, all it says is what $T$ is for a given $\langle x,y,z\rangle$. Nov3 revised Finding the matrix of a linear transformation relative to two non-standard bases Added missing part of question Nov3 asked Finding the matrix of a linear transformation relative to two non-standard bases Nov3 awarded Nice Question Nov3 asked How to find the coordinate vector of $\left[\begin{array}{r}x\\y\end{array}\right]$ with respect to some non-standard basis $\mathcal{B}$ Oct31 awarded Popular Question Oct28 revised If $\mathbb{Z}_m^*$ is cyclic, and $\mathbb{Z}_m^*=\langle\overline{g}\rangle$, is $\overline{g}$ a primitive root? added 41 characters in body Oct28 comment If $\mathbb{Z}_m^*$ is cyclic, and $\mathbb{Z}_m^*=\langle\overline{g}\rangle$, is $\overline{g}$ a primitive root? @ThomasAndrews I meant to imply when it is cyclic; as in, when $m=1,2,4$, or is of the form $p^{\alpha}$ or $2p^{\alpha}$ where $p$ is an odd prime. Oct28 asked If $\mathbb{Z}_m^*$ is cyclic, and $\mathbb{Z}_m^*=\langle\overline{g}\rangle$, is $\overline{g}$ a primitive root? Oct28 comment What are the generators of $\mathbb{Z}_9^*$? @JyrkiLahtonen OK, then from the table alone, assuming I correct it to use multiplication instead of powers, can I find a generator from it? Or do I have to test each one individually with the method above?