If n ⩾ 2 is a positive integer, then the sum of the series C 2 n + 1 + 2 C 2 2 + C 2 3 + C 2 4 +…

If n2 is a positive integer, then the sum of the series C2n+1+2C22+C23+C24++C2n is
  1. nn-12n+16
  2. nn+12n+16
  3. nn+12n+212
  4. n2n+13n+16

Solution

C2n+1+2C22+C23+C24++C2n

C2n+1+2C33+C23+C24++C2n

{use Cr+1n+Crn=Crn+1}

=C2n+1+2C34+C24+C35++C2n

=C2n+1+2C35+C25++C2n

=C2n+1+2C3n+C2n

=C2n+1+2·C3n+1

=n+1n2+2·n+1nn-12.3

=nn+12n+16

Asked in: JEE Main 2021 (24 Feb Shift 2)

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