Question

which method to be used for this sum?

Answer 1

For the limits questions where limit is of the form n tends to infinity, you need to convert the expression in having terms of the form a^(-n). so when n tends to infinity, this will tend to zero.

(2^n -1)/(2^n +1)

Divide it by 2^n

(1-2^-n)/(1+2^-n)
when n->Infinity => 2^-n -> 0

hence the value of expression is 1-0/1+0 = 1

So, option B is correct.