Affiliation: | 1. Nhatrang Educational College, 01 Nguyen Chanh Street, Nhatrang City, Viet Nam;2. Department of Mathematics, University of Economics of Ho Chi Minh City, 59C Nguyen Dinh Chieu Street, Dist. 3, Ho Chi Minh City, Viet Nam;3. Department of Mathematics and Computer Science, University of Natural Science, Viet Nam National University, Ho Chi Minh City, 227 Nguyen Van Cu Street, Dist. 5, Ho Chi Minh City, Viet Nam |