Eigenvalues, Eigenvectors, and Invariant Subspaces — Sheldon Axler
Mathematics — Linear Algebra · upper-triangular-matrices
Problem
Suppose V is finite-dimensional and T∈L(V). Prove that T has an upper-triangular matrix with respect to some basis of V if and only if the dual operator T′ has an upper-triangular matrix with respect to some basis of the dual space V′.