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Apr
12
answered Determine the units of the ring $A= \mathbb Z[X]/(X^3)$ and the structure of the group $A^*$
Apr
6
answered How to prove that $ \sum_{k=1}^{n-1} \frac{1}{1-e^{2 \pi i k/n}} = \frac{n-1}{2}$?
Apr
5
answered If $a_i\geq 0,$ $\sum\limits_{n=1}^\infty a_n$converges, prove $\sum\limits_{n=1}^\infty\frac{a_1+a_2+\cdots+a_n}{n}$diverges.
Apr
1
answered Prove that $ \int_0^\infty (\frac{\sin x}{x})^2 = \frac{\pi}{2}$.
Mar
31
answered Let $|f(z)| \to \infty$ as $|z| \to \infty$, prove that $f(\mathbb{C})= \mathbb{C}$?
Mar
30
answered How do I show $SO(n)$ is open and closed in $O(n)$?
Mar
27
answered If R is a PID, is it true that $R/\ker \phi$ is also a PID?
Mar
22
answered Normal Subgroups of $SU(n)$
Mar
21
answered Every nilpotent left ideal is contained in a nilpotent 2 sided ideal.
Mar
20
answered Why is $\ker\omega$ integrable iff $\omega\wedge d\omega=0$?
Mar
20
answered Proof of Proposition 2.4 in Atiyah-MacDonald
Mar
20
answered Showing when a permutation matrix is diagonizable over $\mathbb R$ and over $\mathbb C$
Mar
19
answered Morphism of vector bundles covering maps of the bases
Mar
19
answered Lie group. How is manifold defined?
Mar
16
answered Equilateral triangle in a circle
Mar
15
answered Is the set $A = \left\lbrace \frac{2^k}{3^l}: k,l\in\mathbb{Z}\right\rbrace$ dense?
Mar
14
answered Understanding an example from Hatcher - cellular homology
Mar
13
answered Show an ideal is a finitely generated projective module via a split exact sequence
Mar
8
answered $d+1$ distinct points of a rational normal curve in $\mathbb{P}^{d}$ are linearly independent
Mar
8
answered Why is $\deg(f)$ well-defined?