ok fail but that's a part of the process
\eqn{∑ n = 0 ∞ f ( n ) ( a ) n ! ( x − a ) n , {\displaystyle \sum _{n=0}^{\infty }{\frac {f^{(n)}(a)}{n!}}(x-a)^{n},} {\displaystyle \sum _{n=0}^{\infty }{\frac {f^{(n)}(a)}{n!}}(x-a)^{n},}