In any triangle, prove that:
59014
Prove that $\sin(2A)+\sin(2B)+\sin(2C)=4\sin(A)\sin(B)\sin(C)$ when $A,B,C$ are angles of a triangle
29935
If $a, b, c, d>0$ and $abcd=1$ prove that an inequality holds true
44912
Prove that $ \overline {A^\complement} = (A°)^\complement $
29679
Prove: $|x-y|\leq |x|+|y|$
128786
How to use triangle inequality to establish Reverse triangle inequality
76635
Proof through combinatorial argument
88605
Proof of the Reverse Triangle Inequality
94091
In $ \triangle ABC$ show that $ 1 \lt \cos A + \cos B + \cos C \le \frac 32$
103806
How to prove triangle inequality for $p$-norm?
156596
Prove $r^2+r_1^2+r_2^2+r_3^2=16R^2-a^2-b^2-c^2$ for a triangle with sides $a$, $b$, $c$, circumradius $R$, inradius $r$, exradii $r_1$, $r_2$, $r_3$
115929
In a triangle $\angle A = 2\angle B$ iff $a^2 = b(b+c)$
88982
Prove that for any two sets $A$ and $B$, $A\notin B$ or $B\notin A$
130722
Can you prove this property?
81003
Given 5 arbitrary points in the plane from which no 3 are collinear, prove that you can always choose 3 that are vertices of obtuse triangle.
22856
Ways to go from A to B(proof)
143735
Prove/Disprove: For any sets $X$ and $Y$, $\overline{X\cap Y} = \bar{X}\cup\bar{Y}$
68986
Use the triangle inequality to show that $|a|+|b| \leq |a+b|+|a-b|$