f ( x ) = ∑ n = 0 ∞ f ( a ) ( n ) n ! ( x − a ) n {\displaystyle f(x)=\sum _{n=0}^{\infty }{f(a)^{(n)} \over n!}(x-a)^{n}}
cas particulier : y ″ − ω 2 y = 0 {\displaystyle y''-\omega ^{2}y=0}
− j ≤ m ≤ + j {\displaystyle -j\leq m\leq +j\,}