Following is the simplest proof I am aware of. M such that angles ACB and MCD be equal. Since angles BAC and BDC subtend the same arc, they are equal. Therefore, triangles ABC and DMC are similar. A 3 denote an equilateral triangle inscribed in a circle.
Solution Let s denote the length of the side of the given triangle.
Remark Ptolemy's theorem is a powerful result. With its help we establish the Pythagorean Theorem . Combined with the Law of Sines , Ptolemy's theorem serves to prove the addition and subtraction formulas for the sine function . Alexander Bogomolny 2789711 .