Geometry problem (proving a relation between sides of a triangle)
72707
Property of Medians and Cirumcircle
101476
If $A$, $B$ and $C$ are the angles of a triangle then find the value of $\Delta$
139065
Proving $\csc\frac\alpha2+\csc\frac\beta2+\csc\frac\gamma2 \ge 6$, where $\alpha$, $\beta$, $\gamma$ are the angles of a triangle
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 $r_1$, $r_2$, $r_3$
84334
How to prove the Pythagoras theorem using vectors
134764
Triangle Inequality question with fractions
123133
If, in a triangle, $\cos(A) + \cos(B) + 2\cos(C) = 2$ prove that the sides of the triangle are in AP
72882
If $a$, $b$, and $c$ are sides of a triangle, then $\frac{a}{b+c}+\frac{b}{c+a}+\frac{c}{a+b}<2$.
88605
Proof of the Reverse Triangle Inequality
73392
How to prove that triangle inscribed in another triangle (were both have one shared side) have lower perimeter?
154274
How many triangles are there in the picture?
5642
Geometry with Trigonometry
23979
Inequality involving sides of a triangle
83788
Condition on sides of triangle to proof it is isoceles
125171
Help with this trigonometry problem?
123465
In triangle $ABC$, $AA_1$, $BB_1$, $CC_1$ divide sides in ratio of $1: 2$ and meet at $M$, $K$, $L$. Find area relation of $KLM$ and $ABC$
21745
Proof of Heron's Formula for the area of a triangle