No maximum(minimum) of rationals whose square is lesser(greater) than $2$.
4552
Choice of $q$ in Baby Rudin's Example 1.1
234
No continuous function switches $\mathbb{Q}$ and the irrationals
148585
Show that, for any $\epsilon>0$, there exist two rationals such that $q < x < q'$ and $|q-q'|<\epsilon$
153798
Problem involving maximum and minimum of a continuous function
34325
Minimizing $\sum_{i=1}^n \max(|x_i - x|, |y_i - y|)$ - Sum of Max of Absolute Values
3885
Maximum and minimum of of $f(x)=|x-1|+|x-2|+|x-3|$
150037
Finding the simplest rational in a closed interval
50172
Show that $\mathbb{Q}(\sqrt{2})$ is the smallest subfield of $\mathbb{C}$ that contains $\sqrt{2}$
3213
There exists only two groups of order $p^2$ up to isomorphism.
115850
Minimum of $|ax-by+c|$
100913
It is impossible for $(x-1)^2+x^2+(x+1)^2$ to be a perfect square
8617
How do you prove ${n \choose k}$ is maximum when $k$ is $ \lceil \tfrac n2 \rceil$ or $ \lfloor \tfrac n2\rfloor $?
141073
Are there fewer positive integers than all integers?
21986
What is the minimum value of $(1 + a_1)(1 + a_2). . .(1 + a_n)$?
33866
Show that $n$ does not divide $2^n - 1$ where $n$ is an integer greater than $1$?
24706
Is there a rational number between any two irrationals?
114810
$n!$ is never a perfect square if $n\geq2$. Is there a proof of this that doesn't use Chebyshev's theorem?