The nifal triangle is the sign of a nifal, YQTL. It consists of the hiriq under the prefix, up to the dagesh in the first letter, and down to the qamats under the first letter. This triangle is the sign of the nifal, YQTL.
יִפָּרֵד
In the even that the first letter is a guttural which does not accept the dagesh, the previous vowel will lengthen as in וַיֵּאָבֵק