Second order differential equation, Frobenious method, Dirac delta function. Gamma and Beta functions, generalized factorials, Euler constant and Weistrass formula. Sturm-Liouville problem, Bessel inequality, Gram-Schmidt orthonormalization, Hermitian operators. Bessel functions, Neuman functions, Hankel functions, spherical Bessel functions. Legendre functions, Rodrigues formula, generating function, spherical harmonic, addition theorem.