GeoDom

 As the title suggests, the half-angle formulas are central . Even more central than the law of cosines, which is nothing more than the half...

 The following problem was proposed by my esteemed friend, Ángel Mejía. However, this is  problem 1315 from Gogeometry . Here I give a trigo...

In a  previous post , we proved an identity about triangle areas arising from reflection. In this occasion, we prove another interesting ide...

 I have noticed experimentally that: $$\int_0^1 \frac{\color{red}{x}}{x^4+2x^3+2x^2-2x+1} \,dx=\color{blue}{\frac{\pi}{8}},\tag{1}$$ $$\int_...

 If you are a student of integral calculus, it is highly likely that you have come across or will come across the famous  Weierstrass substi...

  The following is an extension of the  law of sines for cyclic quadrilaterals that comes to accompany the  generalization of Mollweide...

Several interesting proofs of angle sum identity are given on  MathSE . In this note, I will provide another proof that is possible because,...