If the elastic constants E, k, and are required to be positive, show that Poissons ratio

If the elastic constants E, k, and μ are required to be positive, show that Poisson’s ratio must satisfy the inequality –1 < v < 1/2. For most real materials it has been found that 0 < v < 1/2. Show that this more restrictive inequality in this problem implies that λ > 0.