Δ ABC echilateral , notam AB=BC=AC = a
din M perpend . ⇒ Δ MPA drept cu mas < MAN = 60
M mijloc ⇒ AM = a /2
cos 60 = AP / AM ; 1 /2 = AP / a /2
1 /2 · a /2 = AP ; AP = a / 4
AP + PN = AN , N mijloc ; AN = a /2
a /4 + PN = a /2
PN = a /2 - a /4 = ( 2a - a ) / 4 = a /4 = AC /4