Mathematical Inequalities & Applications · Volume 15, Issue 3 Quadratic inequalities and a characterization of inner product 15-50 Pages 571-580 DOI 10.7153/mia-15-50 Downloads Short PDF Full PDF PNG Authors Janusz Matkowski Keywords parallelogram equality inner product quadratic functional quadratic inequality Jordan-von Neumann theorem Subject classes 46C15 26D15 39B22 39B55