Help proving $\partial (A \cup B) = \partial A\cup\partial B$?
30231
The boundary of union is the union of boundaries when the sets have disjoint closures
102917
Proving statement - $(A \setminus B) \cup (A \setminus C) = B\Leftrightarrow A=B , C\cap B=\varnothing$
154698
Union of Cartesian products: $X \times (Y \cup Z)= (X \times Y) \cup(X\times Z)$
141114
Question about a bijection between $\mathbb R$ and $\mathbb R \cup \{\infty\}$
127656
How to prove that if $A$ is infinite and $B$ is finite, then $|A\cup B|=|A|$?
107383
Derived sets - prove $(A \cup B)' = A' \cup B'$
145966
Find $P(A\ xor\ B\ |\ A\ \cup\ B)$
86977
If $\cup \mathcal{F}=A$ then $A \in \mathcal{F}$. Prove that $A$ has exactly one element.
45363
Show that both mixed partial derivatives exist at the origin but are not equal
20280
Proving that expression is equivalent to the definition of derivative
28416
Show that $\partial_\nu T^{\mu\nu} = - j_\nu F^{\mu\nu}$
24856
Proving sup(A + B) = sup A + sup B
79165
How to show that $P(A\cup B) = P(A) + P(B) - P(A\cap B)$
138199
Proof explanation $A\setminus B = A \setminus B \cap A$
78463
Prove that $\sup \{-x \mid x \in A\} = -\inf\{x\mid x \in A\}$
33030
Proof that $\inf A = -\sup(-A)$
52323
Maps - question about $f(A \cup B)=f(A) \cup f(B)$ and $ f(A \cap B)=f(A) \cap f(B)$