Maths Spéciales (2nd Year French Engineering University Math ”Linear Algebra”): The French way of treating Matrices is very general and abstract. Advantage is it studies Matrices at a theoretical high-level, disadvantage is it ignores on applications.

This young French prof explained in 30 mins at great length of what is simply the Characteristic Polynomial Equation:

$latex boxed {det (A – lambda.I) = 0 }&fg=aa0000&s=3$

Compare it with the more practical (but less theoretical – 知其然而不知其所以然) American teaching below from the famous MIT Prof Gilbert Strang for the same Diagonalization of Matrices: