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voldemort
  • Member for 10 years, 2 months
  • Last seen more than 8 years ago
47 votes

Why is $l^\infty$ not separable?

13 votes

How many maps $\phi:\Bbb{N}\to\Bbb{N}$ are there with $\phi(ab) = \phi(a)+\phi(b)$?

13 votes

Is the composition of irreducible polynomials again irreducible?

13 votes

Show that the ring of continuous functions $f:\mathbb R\to\mathbb R$ is not Noetherian

12 votes
Accepted

Is $C^{\infty}([0,1])$ a Banach space?

11 votes
Accepted

How to show $\displaystyle\lim_{n\to\infty}\sqrt[n]{|z^n|}=|z|$

11 votes
Accepted

Is $f(x)=10$ a periodic function?

10 votes

What's $R[x]/(x^2)$ isomorphic to?

10 votes

Prove that $\sqrt{2 + 9n}$ is never an integer

10 votes

Binomial theorem for matrices

9 votes
Accepted

If $x>0$, $\,x^{1/n}$ tends to $1$ as $n\to\infty$

9 votes
Accepted

$e^x$ defined $a^x$

9 votes

How to maintain enthusiasm and joy in teaching when the material grows stale

8 votes
Accepted

In which Fields, does $x^n-x$ have a multiple zero?

8 votes
Accepted

How to simplify the integral of $\int\frac{\cos(8x)}{\cos(4x)+\sin(4x)}dx$?

8 votes

What's your favorite proof accessible to a general audience?

8 votes

Lebesgue measure of sets of empty interior

8 votes
Accepted

Fourier coefficient of complex measure (Exercise in Rudin)

7 votes

Are $\Bbb R^2$ and $\Bbb R^3$ homeomorphic?

7 votes
Accepted

Best Rigorous Probability Theory Textbook 'without' Measure Theory?

7 votes

Is it possible to find the complex roots of $x^3 + 2 x^2 - 3 = 0$

7 votes
Accepted

Show that $A + A^{-1} \geq 2I$ for $A > 0$.

7 votes

The order of $bab^{-1}$ is equal to the order of $a$ for any $a,b \in G$

6 votes

Compute: as $\displaystyle{\lim_{n\to \infty} \int_0^\pi \sin^n x dx}$

6 votes

Finding the Integer part of $\sum_{k=2} ^{9999}\frac{1}{\sqrt k}$

6 votes

Finding a closed-form formula for a sequence that is defined recursively

6 votes

Show that $1+z=2\cos\frac 12\theta(\cos\frac 12 \theta + i\sin \frac 12 \theta)$

6 votes

how to prove: $\sum\limits_{k=1}^n k\binom{n}{k}=n \cdot 2^{n-1} $

6 votes
Accepted

spectrum of convolution integral operator

5 votes

If $f\circ g = g \circ f$ does that mean that both functions are to and from the same set and both are bijections? Does it tell us anything else?

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