Question

find the sum of n terms of series whose nth term is n(n+3).

Answer 1

n=1 (1+3) =4 n=2 2(2+3)=10 d= 10-4 = 6 an= a = 4 sn=4/2*(2*4+(4-1)6 ) 2*8+18 2*26 =52

Answer 2

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