grandes-ecoles 2014 QI.A.2

grandes-ecoles · France · centrale-maths2__pc Invariant lines and eigenvalues and vectors Diagonalizability determination or proof
Let $s$ be an endomorphism of $E$ such that $s \circ s = \operatorname{Id}_E$. We set $F = \operatorname{Ker}(s - \operatorname{Id}_E)$ and $G = \operatorname{Ker}(s + \operatorname{Id}_E)$. a) Show that $F$ and $G$ are two supplementary subspaces of $E$. b) Deduce that $s$ is a symmetry and specify its elements.
Let $s$ be an endomorphism of $E$ such that $s \circ s = \operatorname{Id}_E$. We set $F = \operatorname{Ker}(s - \operatorname{Id}_E)$ and $G = \operatorname{Ker}(s + \operatorname{Id}_E)$.\\
a) Show that $F$ and $G$ are two supplementary subspaces of $E$.\\
b) Deduce that $s$ is a symmetry and specify its elements.