f(x)=1/x
= 1/[(x-3)+3]
= 1/3*1/[1+(x-3)/3]
= 1/3*∑(n=0,+∞) (-1)^n*[(x-3)/3]^n
= ∑(n=0,+∞) (-1)^n/3^(n+1)*(x-3)^n