Prove that $A \triangle B=B\triangle C\implies A=C$
111003
Prove that if $A\triangle B = C\triangle B$, then $A = C$
142993
Proof of A ⊆ C and B ⊆ C ⇔ A ∪ B ⊆ C
137707
How to prove that $(A\cup B) \cap C \subseteq A\cup (B\cap C)$
109745
If $(a,k)=(b,m)=1$, prove that $(ab,km)=(a,m)(b,k)$.
120094
Prove, that for any A, B, C sets, $A\times (B\setminus C) = (A\times B)\setminus (A\times C)$ is true.
44119
Prove that $\cos (A + B)\cos (A - B) = {\cos ^2}A - {\sin ^2}B$
104217
Alternative triangle inequality proof
153670
Prove that if $a \mid b$ and $b \mid c$, then $a \mid c$.
56399
Proof for $A \cup B = B$ if and only if $A \subset B$
24845
Let $a\mid c$ and $b\mid c$ such that $\gcd(a,b)=1$, Show that $ab\mid c$
137626
If $a,b,c$ are positive integers,and $\cfrac{a}{b}+\cfrac{b}{c}+\cfrac{c}{a}$ and $\cfrac{b}{a}+\cfrac{c}{b}+\cfrac{a}{c}$ are integers then $a=b=c$
80876
Proof of $A\cap(B\cup C) = (A\cap B)\cup(A\cap C)$
11168
Proof of divisibility: if $a|b$ and $a|(b+c)$ then $a|c$
115460
Proving $a\mid b^2,\,b^2\mid a^3,\,a^3\mid b^4,\ldots\implies a=b$ - why is my approach incorrect
125868
Prove $a \equiv b \pmod{c} \implies a^n \equiv b^n \pmod{c}$.
67717
$A \oplus B = A \oplus C$ imply $B = C$?
76680
Prove that if $\gcd(a,c)=1$ and $\gcd(b,c)=1$ then $\gcd(ab,c)=1$