Daniel Fischer's user avatar
Daniel Fischer's user avatar
Daniel Fischer's user avatar
Daniel Fischer
  • Member for 10 years, 8 months
  • Last seen more than 3 years ago
199 votes
Accepted

Why does the google calculator give $\tan 90^{\circ} = 1.6331779e^{+16}$?

143 votes
Accepted

An inequality: $1+\frac1{2^2}+\frac1{3^2}+\dotsb+\frac1{n^2}\lt\frac53$

126 votes

What is the smallest unknown natural number?

63 votes
Accepted

Reflection across a line?

56 votes

Is it possible to solve this equation by hand?

51 votes
Accepted

Mean value theorem for holomorphic functions

49 votes

Why is $(\sqrt{2}+\sqrt{3})^{2008}$ so close to an integer?

48 votes
Accepted

Why is the matrix norm $||A||_1$ maximum absolute column sum of the matrix?

44 votes
Accepted

Proof that one large number is larger than another large number

44 votes
Accepted

Example of a sequence with more than one limit.

42 votes
Accepted

least common multiple $\lim\sqrt[n]{[1,2,\dotsc,n]}=e$

42 votes
Accepted

Proving that $\frac{\pi}{4}$$=1-\frac{\eta(1)}{2}+\frac{\eta(2)}{4}-\frac{\eta(3)}{8}+\cdots$

39 votes
Accepted

If $\sum\frac1{a_n}$ is convergent, then irrational?

39 votes

No cont function $f\colon\mathbb{R}\to\mathbb{R}$ with $f(x)$ rational $\iff f(x+1)$ irrational.

37 votes
Accepted

Fourier transform of the indicator of the unit ball

37 votes
Accepted

Speed of convergence of Riemann sums

37 votes
Accepted

When does equality hold in the Minkowski's inequality $\|f+g\|_p\leq\|f\|_p+\|g\|_p$?

36 votes
Accepted

Does there exist an holomorphic function such that $|f(z)|\geq \frac{1}{\sqrt{|z|}}$?

35 votes
Accepted

Is there no norm in $C^\infty ([a,b])$?

34 votes

Solve the following trigonometric integral

32 votes
Accepted

If every real-valued continuous function is bounded on $X$ (metric space), then $X$ is compact.

32 votes

Examples of uncountable sets with zero Lebesgue measure

32 votes
Accepted

"Integration by parts" in complex analysis

31 votes

Does the rank-nullity theorem hold for infinite dimensional $V$?

29 votes
Accepted

Example of quotient mapping that is not open

29 votes
Accepted

$z_0$ non-removable singularity of $f\Rightarrow z_0$ essential singularity of $\exp(f)$

29 votes
Accepted

Convexity and equality in Jensen inequality

28 votes
Accepted

Help finding a combinatorial proof of $k {n \choose k } = n {n - 1 \choose k -1}$

26 votes
Accepted

Why is this inclusion of dual of Banach spaces wrong?

25 votes
Accepted

Intersection of kernels and linear dependence of functionals

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