Corollary 5
Tag 00NO, permanent. Cite it as [Bourbaki, Tag 00NO].
Algebra, VIII, p. 402, § 21. Linear Representations of Finite Groups
Suppose that the group G is finite and that K is a commutative field in which . Let and be finite-dimensional linear representations of G. Then and are isomorphic if and only if for every in G, the endomorphisms and have the same characteristic polynomial.
This follows from Corollary 1 of VIII, p. 386.
Bourbaki sets the proof directly after the statement, and the corpus does not separate them, so what is above is the statement and its proof together.