“…In this connection, readers are referred to Chaudhry et al (1987), Chaudhry et al (1990), Tijms (2003) and Chaudhry et al (2012Chaudhry et al ( , 2013, who have used the roots method. In particular, regarding the details about the use of Rouché's theorem in the analysis of characteristic equation, the readers are referred to Cohen and Down (1996), Adan et al (2006) etc.…”