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 May19 comment Why having $ma+np=1$ implies that $m$ is the inverse? Yes. Every multiple of $mp$ of $p$ puts $mp$ in the same class of equivalence, namely $mp=\overline{0}$, then $ma+\overline{0}=1$. I guess I get it now. May19 comment Why having $ma+np=1$ implies that $m$ is the inverse? What do you mean with $[]$? May17 comment A silly problem on critical points? @zhw. So those critical points are complex critical points? May17 comment A silly problem on critical points? @zhw. Then why Wolfram Alpha says there are critical points? May17 comment A silly problem on critical points? @John Yes. But the problem is that it seems that it's possible to do some magic and use it. Mathematica solves $\sin(x)=2$ as {{x -> ConditionalExpression[\[Pi] - ArcSin[2] + 2 \[Pi] C[1], C[1] \[Element] Integers]}, {x -> ConditionalExpression[ArcSin[2] + 2 \[Pi] C[1], C[1] \[Element] Integers]}}. May17 comment A silly problem on critical points? @John From the page: "$Sin^{-1}(x)$ is the inverse sine function." May17 comment A silly problem on critical points? @John See here. May14 comment If $n^2=ab$ and $\gcd(a,b)=1$, show that $a,b$ are not necessarily squares. And the author actually gave a similar hint in the beginning of the questions and I completely missed it. I'm so stupid. May14 comment If $n^2=ab$ and $\gcd(a,b)=1$, show that $a,b$ are not necessarily squares. Oh. $-1\cdot -1$ and $1 \cdot 1$. I guess I understand it. May14 comment If $n^2=ab$ and $\gcd(a,b)=1$, show that $a,b$ are not necessarily squares. @HenningMakholm I explained a little further in the text. May14 comment In a ring, if addition is commutative, does it implies that multiplication is commutative? @RobertLewis No. See my profile for explanation. May14 comment In a ring, if addition is commutative, does it implies that multiplication is commutative? Of, it seems I confused one thing. Here. He says: "In addition, if $ab=ba$, then it is a commutative ring". I thought he was talking about addition. Silly me. May14 comment What is $R(k,l)$? Oh, now I get it. Thanks. May6 comment Why can't we eliminate $t$? @MatemáticosChibchas Yes, my child. I am very fond of this song, you should be too. Apr27 comment At which points the tangent lines of the function $y=\cos x$ are parallel to $-\frac{1}{2}x+1$? @user37238 Yes! I guess you helped me to find the silly mistake. Let me write it. Apr27 comment At which points the tangent lines of the function $y=\cos x$ are parallel to $-\frac{1}{2}x+1$? @user37238 When I evaluate $-\sin x=- 1/2$, I'd have the pair $(\pi/6,-1/2)$. The first item of the pair is $x$, the second one is $y$. I just made the substitution. Apr20 comment How to show that \$0