## 4 Discussion of the Results  
Throughout the content analysis of the articles, we need to go back to the aim of this study, which is to identify challenges, technical problems, and benefits of applying AR within the five areas selected. Firstly, we have identified that AR used as an educational tool is a prevalent topic which easy to find in any of the chosen databases; this is because helping students to become actively involved in their classes is a concern for any educational institution. The benefit of AR in the classroom is the production of dynamic environments [72] where motivation and interaction are the main features [73]. Within this study, we observed some AR applications in educational games that were successfully applied and tested for children of different ages and school levels [74]. AR has shown along the way that it is a tool with a positive impact within schools or training areas where characteristics of inspiration for learning, satisfaction, and confidence are prominent [14; 21; 22; 25; 27; 29]. Finally, we discovered that AR was useful in understanding abstract concepts difficult to manage with normal classroom tools in subjects such as physics [24; 27]. Talking about AR challenges in this area, we could find that when authors made tests to prove if AR was effective in learning, unfortunately, they discovered that even though the understanding was good, the improvements in knowledge retention were minimal [26; 27], so it is still necessary to keep working on making AR for meaningful learning. Another task to be solved is the lack of professionalization in teachers because before using AR tools it is necessary to train school personnel, as well as to have easy AR application methodologies and manuals to make AR easy to manage at school. Besides that, educational institutions must invest in technological infrastructure [14; 22]. Despite the difficulties that emerged, there are still studies that considered possible solutions, but still with no promising results [24]. The technical problems in the studies of AR in education were mostly the lack of robust infrastructure to support the AR systems. AR is commonly applied in industry. It is noticed that aviation, industrial and automotive plants are fields with more AR implementation [75]. It is important to highlight that a large percentage of its use refers to the mechanical area, justifying the data by its usage in areas such as automotive, training, and military industries, among other aspects of general mechanical operations. Moreover, technical processes in industries constantly need to be monitored and this is where AR shows us that it is the ideal tool to reduce errors and production times [15; 31; 35; 36; 38] as well as train staff with manuals and machinery tools labeling [12; 34; 37]. Nevertheless, in the technical problems found, we noticed that it is necessary to implement optimal processes by selecting the appropriate programming frameworks [32] to reduce latencies along with the difficulty of lighting and precision [32; 33; 34]. In the same way, it is essential to look for ergonomic, specialized, and easy-to-use hardware involved in ARI to eradicate the user's lack of comfort [33]. The challenge of AR in this area is the creation of new manual content to make functions that manage and develop industrial processes within the industry [38]. An innovative way of reaching new clients in marketing is the use of AR in the delivery of promotional messages personalized with greater precision, working through geolocation and individualized adaptation to create confidence and the intention to purchase [76]. The interaction with products thanks to AR is dynamic in making the decision to purchase [77]. Companies are taking advantage of the information gathered thanks to the use of AR applications in marketing and in creating customer profiles to follow-up [78].