Source: https://www.researchgate.net/profile/Syham-Kadri/publication/325158021_Vibrations_et_Ondes_F312_Cours_et_Exercices_Corriges_Partie_I_Vibrations/links/5afb471ea6fdccacab1918c2/Vibrations-et-Ondes-F312-Cours-et-Exercices-Corriges-Partie-I-Vibrations.pdf