Question: Let $T : V → V$ be a unitary linear transformation on a finite-dimensional inner product space V . Let $W ⊂ V$ be a $T$-invariant subspace. Prove that $T(W) = W$ and $T(W^⊥) = W^⊥$
Having a lot of trouble with this question and don't know where to start. Can someone lend me a hand?