QUADRATIC ρ-FUNCTIONAL INEQUALITIES IN BANACH SPACES.

In this paper, we solve the following quadratic ρ-functional inequalities ‖f (x + y + z/2) + f(x - y - z/2) + f(y - x - z/2) + f(z - x - y/2) -f(x) - f(y) - f(z)‖ ≤ ‖ρ(f(x + y + z) + f(x - y - z) + f(y - x - z) + f(z - x - y) (0.1) -4f(x) - 4f(y) - 4f(z))‖; where ρ is a fixed complex number with |ρ| < 1/8, and ‖f(x + y + z) + f(x - y - z) + f(y - x - z) + f(z - x - y) -4f(x) - 4f(y) - 4f(z)‖ (0.2) ≤ ‖ ρ(f(x + y + z/2) + f(x - y - z/2) + f(y - x - z/2) + f(z - x - y/2) -f(x) - f(y) - f(z))‖ ; where ρ is a fixed complex number with |ρ| < 4. Using the direct method, we prove the Hyers-Ulam stability of the quadratic ρ-functional inequalities (0.1) and (0.2) in complex Banach spaces and prove the Hyers-Ulam stability of quadratic ρ-functional equations associated with the quadratic ρ-functional inequalities (0.1) and (0.2) in complex Banach spaces. [ABSTRACT FROM AUTHOR]