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 Apr 2 awarded Yearling Dec 22 awarded Enlightened Dec 22 awarded Nice Answer Apr 2 awarded Yearling Mar 27 awarded Popular Question Sep 13 awarded Good Question Apr 2 awarded Yearling May 2 awarded Nice Answer Apr 15 awarded Enlightened Apr 15 awarded Nice Answer Apr 2 awarded Yearling Jun 2 comment Determining the derivative of $e^{5x}\tan(2x)$ shouldn't $g(x) = \tan(2x)$? May 30 comment Product of two ideals doesn't equal the intersection @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. May 30 comment Product of two ideals doesn't equal the intersection @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 $J$. May 29 comment Product of two ideals doesn't equal the intersection @Dylan Moreland: Thanks for your comment! I just edited my answer. May 29 revised Product of two ideals doesn't equal the intersection deleted 21 characters in body May 29 answered Product of two ideals doesn't equal the intersection May 29 answered Simple Set Theory Question May 28 comment Duality of $L^p$ and $L^q$ @t.b. Thank you for your comment and for the link. I appreciate it. May 28 answered Duality of $L^p$ and $L^q$