Negation of x in A or B

Hi all,

if no means the negation of a condition.

no( $x \in ( \mathbf{A} \cup \mathbf{B})) \Longleftrightarrow (x \not \in \mathbf{A}) \cap (x \not \in \mathbf{B})$

this is right, right?

But
no( $x \in ( \mathbf{A} \cup \mathbf{B})) \Longleftrightarrow x \not \in (\mathbf{A} \cap \mathbf{B})$

is wrong, right?