# Math Help - about diagonalisable

also not sure about when a matrix is diagonalisable.
my director only tells that if the geo. multiplicity equal to algebraic multiplicity.

but... any other idea about when :

it is not diagonalisable over C
not diagonalisable over R
not diagonalisable over R , but diagonalisable over C
diagonalisable over R but not have an orthonormal basis of eigenvectors