notam VABCD piramida patrulatera
VO=inaltimea
AB=BC=CD=AD=L
AC=BD=diagonale baza
O intersectia diagonalelor baze
Pitagora in triunghiul VOA
AO=√[15²-(3√7)²]=√(225-63)=√162=9√2
AC=9√2 × 2=18√2
AC²=AB²+BC²=2L²
AC=L√2
18√2=L√2
L=18
apotema bazei=18/2=9
apotema piramidei=√(15²-9²)=√(225-81)=√144=12
