f(x)=1/x
=-1/[1-(x+1)]
=-[1+(x+1)+(x+1)²+...+(x+1)^n]+[f(ζ)^(n+1)×(x+1)^(n+1)]/(n+1)!
f(x)=e^(-x)
=e^[-(x-a)-a]
=e^(-a)×e^[-(x-a)]
=e^(-a)×[1-(x-a)+(x-a)²/2!+...+(-1)^n(x-a)^n/n!]+o((x-a)^n)