In this paper, we generalize the main results of [Effros EG, (2009) Proc Natl Acad. Sci USA 106:1006–1008]. Namely, we provide the necessary and sufficient conditions for jointly convexity of perspective functions and generalized perspective functions.

We obtain the general solution and the generalized Ulam‐Hyers stability of the mixed type cubic and quartic functional equation f(x + 2y) + f(x − 2y) = 4(f(x + y) + f(x − y)) − 24f(y) − 6f(x) + 3f(2y) in quasi‐Banach spaces.

In this article, we study the impact of teamwork on an organization’s performance, considering a cooperative game’s framework. To promote teamwork culture, performance indexes were considered both individually and collectively, and by comparing the scores that every employee earned individually and collectively, their differences became obvious. In this approach, a cooperative game’s model was used in order to improve the organization’s performance. The proposed model, in addition to evaluating the organization and employee’s activities, implemented all payments, including overtime pay, rewards, etc., fairly and along with increasing performance and satisfaction. The cooperative approach created effective communications between employees and authorities and enhanced their motivation for teamwork. Moreover, results could be used for decisions related to employees (such as promotion, transition, firing, and secondment), analysis of training requirements, employees’ development, and research and plan valuation. Our findings show that the collaborative coefficient (CC) is a key factor in increasing productivity and improving the efficiency of an organization in the long run. The collaborative coefficient is a new concept in teamwork that has rarely been considered in scientific research.