In this paper we proof the Andrica-Iwata's inequality for a hyperbolic triangle

In this paper, we present a proof of some hyperbolic theorems in the Poincar´e Model of Hyperbolic Geometry.

A geometric approach of Blundon's inequality is presented. Theorem 2.1 gives the formula for cosION in terms of the symmetric invariants s , R, r of a triangle, implying Blundon's inequality (Theorem 2.2). A dual formula for cosIaONa is given in Theorem 3.1 and this implies the dual Blundon's inequality (Theorem 3.2). As applications, some inequalities involving the exradii of the triangle are presented in the last section.