Question

Let B be a 4×4 diagonal matrix, and let WB be the set of 4×4 matrices which
commute with B (i.e., those matrices A so that AB = BA).
(a) Check that WB is a a subspace of M4×4(R).
(b) What is dim(WB)?

Answer 1

I don't know the answer though what is R

Answer 2

M4×4(R)??

Answer 3

its just the the set of real numbers

Answer 4

\[\mathbb{R}\]