MathDB
A pair of matrices

Source: Romanian District Olympiad 2014, Grade 11, P1

June 15, 2014
linear algebra

Problem Statement

[*]Give an example of matrices AA and BB from M2(R)\mathcal{M}_{2}(\mathbb{R}), such that A^{2}+B^{2}=\left( \begin{array} [c]{cc} 2 & 3\\ 3 & 2 \end{array} \right) . [*]Let AA and BB be matrices from M2(R)\mathcal{M}_{2}(\mathbb{R}), such that \displaystyle A^{2}+B^{2}=\left( \begin{array} [c]{cc} 2 & 3\\ 3 & 2 \end{array} \right) . Prove that ABBAAB\neq BA.