u can use the fact that 1/(1-x)=1+x+x^2+x^3+..
so 1/(1-x^2)=1+x^2+x^4+...
now if u have read truncation rule
u can take first three terms only and rest can be assigned as O(x^n)
this would give u the approximated result
u can use the fact that 1/(1-x)=1+x+x^2+x^3+..
so 1/(1-x^2)=1+x^2+x^4+...
now if u have read truncation rule
u can take first three terms only and rest can be assigned as O(x^n)
this would give u the approximated result