how to find number of terms in gp

Question

(2ⁿ⁻²+2ⁿ⁻³+⋯+2²+2+1) how to find sum?

Answer 1

n-2+1 terms 

Comments

To  find sum  ,

$(a(r^{n}-1)) / (r-1)$

a= 1 , r=2   , n = number of term = k = n-2+1

sum = $(1(2^{n-2+1}-1)) / (2-1)$

= $2^{n-1} -1$

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sumit goyal 1 thanks a lot bhai

also, i have seen your message but I am not contempt to solve that as you can see I am at beginners level taking guidance from senior members like you.