the sum of the first n terms of an ap is given by n square + 8n its 12th term
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S1=sum of first term (s)=a1.......hope it helps
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Answer:
Sn = n² + 8n
Sn-1 = (n -1)² + 8(n -1)
we know ,
Tn = Sn - Sn-1
= n² + 8n - (n-1)² - 8(n - 1)
= 2n -1 + 8
= 2n + 7
hence, Tn = 2n + 7
so, 12th term (T12) = 2(12)+7 = 31
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