1.

Let a_1 , a_2 ,a_3, …., a_n be an A.P. and S_1 , S_2 and S_3 be the sum of first n , 2n and 3n terms respectively then S_3 - S_2 -S_1 is equal to , if a is first term and d is common difference :

Answer»

3a-2n-d
a(n+2d)
3a+2nd
`2n^2d`

ANSWER :D


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