ABSTRACT
The urgency of this research is to complement the theory of metacognitive failure to reveal the barriers to face-to-face mathematics learning. This research used a qualitative approach with a case study design. The subjects of this research have passed the Linear Program course, called S1 and S2. S1 who was at level 3 (strategic use) and S2 who was at level 1 (tacit use) both experience ED at the final stage of problemsolving. This ED causes partial metacognitive blindness. Metacognitive blindness only occurs when interpreting the results of the graph where the subject does not realize that the solution to the linear inequality that he does is infinite. The subject incorrectly identified the area that intersects the system of linear inequalities. Therefore, this phenomenon is referred to as partial metacognitive blindness. Partial metacognitive blindness is a special form of metacognitive blindness caused by the appearance of redflags in the verification stage. ED that occurs in S1 and S2 is caused by a lack of cognitive involvement during online learning. In this study, the use of technology, namely GeoGebra, cannot solve the problem. Therefore, further studies are needed especially regarding what prerequisites must be met by students before they use GeoGebra in learning.