proof that $A \triangle (B \triangle C) = (A \triangle B) \triangle C $
12459
Associativity of symmetric difference of sets
86378
Prove that $3(a^3+b^3+c^3) > (a+b+c)(a^2+b^2+c^2)$
56878
Proof that $a\mid b \land b\mid c \Rightarrow a\mid c $
15365
Proving that the triangle inequality holds for a metric on $\mathbb{C}$
139111
Prove that $a<c<b$, $\frac{f(b)-f(a)-(b-a)f'(a)}{g(b)-g(a)-(b-a)g'(a)}=\frac{f"(c)}{g"(c)}$
83475
Prove Or Disprove: tr(AB)=tr(A)*tr(B)
113641
Suppose the gcd (a,b) = 1 and c divides a + b. Prove that gcd (a,c) = 1 = gcd (b,c)
142993
Proof of A ⊆ C and B ⊆ C ⇔ A ∪ B ⊆ C
104217
Alternative triangle inequality proof
12646
In acute angle triangle, prove that $\cos (A-B) \cos (B-C) \cos (C-A)\ge 8\cos A \cos B \cos C$
19457
Show that: $\inf(A+B) = \inf(A)+ \inf(B)$
40596
Proving a relation between inradius ,circumradius and exradii in a triangle
139841
Proving $A\setminus(B\setminus C)$ is not equal to $(A\setminus B)\setminus C$
151038
How to prove (A v B), (A → C), (B → D) therefore (C v D)
68986
Use the triangle inequality to show that $|a|+|b| \leq |a+b|+|a-b|$
134652
Prove that the perpendicular bisectors of the sides of a triangle meet at a point
100895
Prove $1 + \cos 2C - \cos 2A - \cos 2B = 4\sin A\sin B\cos C$ for $A$, $B$, $C$ the angles of a triangle