Q. 12

# Find the sum of coefficients of two middle terms in the binomial expansion of (1 + x)2n-1

Given:

Total terms after expansion = 2n-1+1=2n

Middle term = 2n/2 = nth term

So two required middle terms are : nth & (n+1)th term

k= (n-1) & n for both terms respectively. (1 + x)2n-1 Coefficient of nth term;

=2n-1Cn-1

Coefficient of (n+1)th term ;

= 2n-1Cn

Sum of coefficients = 2n-1Cn-1 + 2n-1Cn

= 2n-1+1Cn

=2nCn

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