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 Apr2 awarded Yearling Mar27 awarded Popular Question Sep13 awarded Good Question Apr2 awarded Yearling May2 awarded Nice Answer Apr15 awarded Enlightened Apr15 awarded Nice Answer Apr2 awarded Yearling Jun2 comment Determining the derivative of $e^{5x}\tan(2x)$ shouldn't $g(x) = \tan(2x)$? May30 comment product of two ideals @Andrew As an example, $2\mathbb{Z} + 3\mathbb{Z} = \mathbb{Z}$ because we can write $1 = 4 + (-3)$ and the first summand belongs to $2 \mathbb{Z}$ and the second one belongs to $3 \mathbb{Z}$. On the other hand, $4\mathbb{Z} + 6 \mathbb{Z} \neq \mathbb{Z}$. Any element of $4 \mathbb{Z} + 6\mathbb{Z}$ is of the form $4x+6y$ for some integers $x,y$; in particular, it is always even so it can never be equal to $1$. I hope this helps. May30 comment product of two ideals @Andrew But $I+J = R$ is a condition on $I$ and $J$! In general, $I+J$ is an ideal of $R$ which may or may not be equal to $R$.An equivalent way to state this condition is that $1 = i + j$ for some $i \in I$ and some $j \in J$. That is, $I+J=R$ if and only if you can write $1$ as a sum of an element of $I$ and an element of $J$. May29 comment product of two ideals @Dylan Moreland: Thanks for your comment! I just edited my answer. May29 revised product of two ideals deleted 21 characters in body May29 answered product of two ideals May29 answered Simple Set Theory Question May28 comment Duality of $L^p$ and $L^q$ @t.b. Thank you for your comment and for the link. I appreciate it. May28 answered Duality of $L^p$ and $L^q$ May27 answered Is this $\left|\left(\frac{a}{b}\right)^n-\left(\frac{a}{b}\right)^{n-1}\right|$ bounded? May20 comment Is the determinant of a matrix lower when all its elements are lower? If $A$ and $A'$ are stochastic, then $A = A'$ as Marvis showed in the response above. May20 comment Is the determinant of a matrix lower when all its elements are lower? It looks like we came up with the same example:-)