This document presents a derivation of the relationship between three elastic moduli: Young's modulus (E), bulk modulus (K), and shear modulus (G). It begins by introducing Hooke's law and defining the three elastic moduli based on the type of stress and strain. It then presents the main result - an equation relating E, K, and G with an arbitrary angle φ. The derivation considers a two-dimensional body under shear stress and calculates the strain produced. It then extends this to a three-dimensional body under multi-axial stresses to relate the elastic moduli and Poisson's ratio. Eliminating Poisson's ratio produces the final relationship between E, K, and G.