E.O. Effanga, J.A. Ugboh, E.I. Enang and B.E.A. Eno
Journal of Modern Mathematics and Statistics 3 ( 4 ): 69 - 72 , 2009
M.E. Nja, E.I. Enang, A.U. Chukwu and C.A. Udomboso
Journal of Modern Mathematics and Statistics 5 ( 2 ): 43 - 46 , 2011