How I can start this problem?
$ X $ is unitary space. Prove that if $M_1, M_2 \subset X: $ $M_1\neq \emptyset ,M_2\neq \emptyset$ and $ M_1 \subset M_2 $ then $ M_2^\perp \subset M_1^\perp $
Thank you in advance
How I can start this problem?
$ X $ is unitary space. Prove that if $M_1, M_2 \subset X: $ $M_1\neq \emptyset ,M_2\neq \emptyset$ and $ M_1 \subset M_2 $ then $ M_2^\perp \subset M_1^\perp $
Thank you in advance
Directly (fill in details):
$$x\in M_2^\perp\implies \langle x,m_2\rangle=0\;,\;\forall\,m_2\in M_2\implies$$
this is true, in particular, for all $\;m_1\in M_1\subset M_2\implies x\in M_1^\perp\;$