S.Alansari, Luay, et al. “Calculating the Natural Frequency of Cantilever Tapered Beam Using Classical Rayleigh, Modified Rayleigh and Finite Element Methods”. International Journal of Engineering & Technology, vol. 7, no. 4, Feb. 2019, pp. 4866-72, https://doi.org/10.14419/ijet.v7i4.25334.