1.

If `S_n,` denotes the sum of `n` terms of an `A.P.`, then `S_(n+3)-3S_(n+2)+3S_(n+1)-S_n=`A. `2s_n`B. `S_(n+1)`C. `3S_n`D. 0

Answer» Correct Answer - D
`S_(n+3)-3S_(n+2)+3S_(n+1)-S_(n)`
`=(S_(n+3)-S_(n+2))-2(S_(n+2)-S_(n-1))+(S_(n+1)-S_(n))`
=`T_(n+3)-2T_(n+2)+T_(n+1)`
`=(T_(n+3)-T_(n+2))-(T_(n+2)-T_(n+1))`
=d-d=0


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