N.M.A. Nik Long, M. Suali, A. Ishak, N. Bachok and N.M. Arifin
Journal of Applied Sciences 11 ( 20 ): 3520 - 3524 , 2011
N.Z. Abidin, N.M. Arifin and M.S.M. Noorani
Journal of Mathematics and Statistics 4 ( 1 ): 1 - 8 , 2008