Respuesta :

In the pyramid PY is the height of the slant faces which is 6 cm, while XY is half of the length, therefore 6/2 = 3 cm
Thus, considering triangle PXY;
PX is the vertical height, and using Pythagoras theorem;
 PX= √(6²-3²) 
     = √ (27)
     = 5.19 cm