New posts in Quadratic Forms

Is the representation of any prime of the form $6n+1$ as $a^2+3b^2$ essentially unique?

Class Group of the Class Number $3$ with their elements given explicitly

If a matrix $A \in \mathbb{R}^{N\times N}$ is both row and column diagonally dominant, will it satisfy $(x^{2p-1})^T A x \geq 0, p \geq 1$?

What are all possible positive integers $k$ such that $k=\frac{a^2+b^2+c^2}{bc+ca+ab}$ for some positive integers $a$, $b$, and $c$?

What is the image of $x^{\rm T}Qx\le 1$ under a linear map $x \mapsto Cx$?

Showing a system of equations has no integer solutions

Convexity of $\{x\in \mathbb R^n,\;x^TAx\leq t\}$ for all $t$ implies that $A$ is p.s.d.

Prove that if $\sum_{i=1}^n x_i=0$ and $\sum_{i=1}^n x_i^2=1$ there exist $i,j$ such that $x_ix_j\leq -{1\over n}$

Why Study Quadratic Forms?

$k\sum v_i v_i^T-\big(\sum v_i\big)\big(\sum v_i^T\big)\succeq 0$