1. The problem statement, all variables and given/known data Suppose a mass- spring is modeled by x''+ cx'+100x. What should the damping constant c be in order that critical damping occurs? 2. Relevant equations 3. The attempt at a solution I set the discriminant equal to zero so that there are real repeated roots. B^2-4ac=0 c^2=400. c=20 or c=-20. The answer should only be c=20. For critical damping, the constant must be positive?