1. The problem statement, all variables and given/known data For a plane stress condition (stress z-axis = 0 ), prove the following relations if strain x-axis and strain y-axis are determined by experiments. σ_x=(∈_x+v∈_y/1-v^2)E & σ_y=(∈_y+v∈_x/1-v^2)E where: σ_x = stress in x-axis σ_y = stress in y-axis ∈_x = strain in x-axis ∈_x = strain in y-axis E = modulus of elasticity 2. Relevant equations ∈_z=-(∈_x+∈_y)(v/1-v) Poission's ratio ∈_x=σ_x/E ∈_y=∈_z=-vσ_x/E v=-lateral strain/axial strain v=-∈_y/∈_x=-∈_z/∈_x 3. The attempt at a solution I'm not sure which equations I should be using to solve the problem. Can I use Hooke's Law for multi-axial loading since it is a plane stress condition? I have tried rearranging Poisson's ratio equation with no luck.