Series[1/(1-x),{x,0,10}]

Series[1/(1-a x),{x,0,10}]

Series[x/(1-x)^2,{x,0,10}]

Series[a/(1-x)+d x/(1-x)^2,{x,0,10}]

Series[1/(1-x -x^2),{x,0,10}]

Series[1/(1-x -x^2-x^3)-,{x,0,10}]

N[100/89,15]

Expand[2(n+1)^2 -3(n+1) +1 -(2(n)^2-3(n)+1)]