Reverse inequality of triangle inequality and a generalization

In this study, we derive a reverse inequality of the triangle inequality under various conditions. It is important that the condition is natural and is related to the meaning of original inequality. We introduce an extension of Pythagorean theorem in order to understand the necessity of the condition. The concept of convex and concave functions are related to our consideration of reverse inequality. These novel reverse inequalities are interesting and provide in-depth understanding of the original inequalities