Deduce relations between sides of a triangle if $\cos A + \cos C= 2 - 2\cos B$
123133
If, in a triangle, $\cos(A) + \cos(B) + 2\cos(C) = 2$ prove that the sides of the triangle are in AP
151038
How to prove (A v B), (A → C), (B → D) therefore (C v D)
68090
Can we find incentre of a triangle by using equation of lines?
23979
Inequality involving sides of a triangle
79
Find $a$, $b$ and $c$ that satisfy the following equations
128006
How to get ratio of a,b,c from 2 equations in a,b,c
43605
If $\sin(a)\sin(b)\sin(c)+\cos(a)\cos(b)=1$ then find the value of $\sin(c)$
68986
Use the triangle inequality to show that $|a|+|b| \leq |a+b|+|a-b|$
149686
Combinatorics and trigonometry identity
23080
Prove that $a^2(b+c-a)+b^2(a+c-b)+c^2(a+b-c) \leq 3abc.$
127004
Extreme of $\cos A\cos B\cos C$ in a triangle without calculus.
63679
Picture/intuitive proof of $\cos(3 \theta) = 4 \cos^3(\theta)-3\cos(\theta)$?
109318
Equivalence relation $(a,b) R (c,d) \Leftrightarrow a + d = b + c$
14410
If $(1+ \cos A) (1+ \cos B) (1+\cos C)= y = (1- \cos A) (1-\cos B) (1-\cos C)$ then $y = \pm \sin A \sin B \sin C$
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 $r_1$, $r_2$, $r_3$
150738
Proof of $(A - B) - C = A - (B \cup C)$
120444
Trigonometric Triangle Equality