1. The problem statement, all variables and given/known data The total cross section of a S wave is given by the following equation Sigma=(pi/k)*(b^2)/((E-En)^2+(b/2)^2)) prove that b is the width of the resonance. 2. Relevant equations Nothing that is the only thing 3. The attempt at a solution I already solved the question using basic calculation. For E=En i get the maximum of Sigma , for half of that maximum , i get a second degree equation of E, when solving it i get 2 solution representing that half maximum(E1 & E2) , the difference between E1 and E2 , E1-E2=b But I'm not really comfortable with the way i did it , I know i got the solution , but i'm looking for another way , something more to do with physics. idea anyone?