The teacher is asking the students to see different closed figures having only four sides, it may help them to conclude that, all those figures have four sides and are closed. Seeing similar figures on various occasions (particular cases) would help them to generalise and develop a new concept i.e. those figures have four sides and are closed;  such figures are called quadrilaterals. Thus experiences with particular cases will broaden the abstractness and help individuals to arrive at a general concept. The teacher is trying to follow which teaching maxim?