I learned about series recently. I noticed a slight similarity between a geometric series
and a integral, say
can you solve using a series instead of trig sub?
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