### Questions (82)

 6 Find all rational points on $x^2 + y^2 = 17$ 6 Finding all the subgroups of the quaternions 6 Proving symmetric matrices are diagonalizable 5 Let $\phi$ be Euler's totient function, find all $n$ such that $\phi(n) = \frac{1}{3} n$. 4 Explaining whether a function is injective/surjection ($f\colon\Bbb N\to P(\Bbb N)$)

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 1 Finding normal subgroups of the symmetry group of the cube 0 Show $\left \lfloor{x}\right \rfloor + \left \lfloor{y}\right \rfloor \leq \left \lfloor{x+y}\right \rfloor$ for every $x, y \in \mathbb{R}$ 0 Proving inequality..

### Tags (82)

 1 group-theory × 17 0 proof-verification × 17 1 normal-subgroups × 2 0 sequences-and-series × 13 1 symmetry 0 finite-groups × 11 0 real-analysis × 23 0 limits × 8 0 elementary-number-theory × 18 0 linear-algebra × 7

### Bookmarks (7)

 26 Proof of $\frac{(n-1)S^2}{\sigma^2} \sim \chi^2_{n-1}$ 25 Prove that a function whose derivative is bounded is uniformly continuous. 17 Let $(x_n)$ be a bounded but not convergent sequence. Prove that $(x_n)$ has two subsequences converging to different limits. 6 Proving $1 > 0$ using only the field axioms and order axioms 5 If $f'$ is increasing and $f(0)=0$, then $f(x)/x$ is increasing [duplicate]