From group 3, ict 2 pere at Olongapo City National High School, Ict in the Philippines, we had the following picture as a suggestion for the completion.
We had, from Harry at Stonebroom, the following:
I think that every side will have a triangle to make it a star
and from Ayesha from Gag in Pakistan we received this similar suggestion:
On the plan side we will add a triangle because it will be in the same form
from every side