Explicitly calling `factorial`

and computing powers of `x`

*separately* for each term in a Taylor series is not a good approach. Not only is this very slow (you have a lot of redundant computations!), but it can also overflow to `0*Inf`

if you compute enough terms.

See, for example, the new implementation of the `cosc`

function in Base for an example of how to compute a Taylor series iteratively (to arbitrary precision), with specialized cases (`evalpoly`

with hardcoded coefficients to a fixed order) for single and double precision.