and A big triangle is bisecting two times in this way as first by perpendicular from top P to base QR making Q K and KR.

and other is Q S that is bisecting the triangle( showed in dotted lines in my book ) length PR A at point S, now the length PR becomes PS and RS, and Q S is making two two more triangles.

the perpendicular is cutting the QR at point k and making two triangles and the line Q S is cutting the the PR at point S , It means 4 triangles has been made within a big triangle and the PK From top to bottom is showed by dotted and Q S that is bisecting
the PR is also shown by dotted lines.

thank you