The sum of n terms of an ap is 3n²+5n.find the ap and hence find its

1.	The sum of n terms of an ap is 3n²+5n.find the ap and hence find its 16th terms
Answer» Given: Sn\xa0= 3n2\xa0+ 5n{tex}\\therefore{/tex}\xa0S1\xa0= 3(1)2\xa0+ 5(1) = 8{tex}\\Rightarrow{/tex}\xa0a1\xa0= 8 ..(i)S2\xa0= 3(2)2\xa0+ 5(2) = 22{tex}\\Rightarrow{/tex}\xa0a1\xa0+ a2\xa0= 22{tex}\\Rightarrow{/tex}\xa08 + a2\xa0= 22 [using (i)]{tex}\\Rightarrow{/tex}\xa0a2\xa0= 14d = a2\xa0- a1\xa0= 14 - 8 = 6AP is 8, 14, 20, 26, ...Now, a16\xa0= a + 15d= 8 + 15(6) = 98

Discussion