Suppose that $B \in R^{n \times n}$ is a symmetric matrix.
How do I prove that if $B$ can be diagonalized, then there must be an orthonormal basis ($v_1,v_2, \dots, v_n$) of eigenvectors of $B$?
This is different than the question tagged as duplicate because I am asking for a proof for that there must be an orthonormal basis rather than just proving vectors are orthogonal.