Geometry

6

@doubt
use vector.
take p as 0 vector. and write other vertices as a,b,c
else use ptolemy inequality.

@doubt
take the Euclidean plane with the complex plane. Let ๐,๐,๐ be the complex numbers corresponds to ๐ด,๐ต,๐ถ respectively.
T. Hayashi, Two theorems on complex number, Tรดhoku Math. J., 4 (19131914), 68โ70