Question

In an A.P, if sn=n^2 +8n then tn​

Answer 1

Sn= n²+8n

S(n-1) = (n-1)²+ 8(n-1)

= n²-2n+1 + 8n-8

= n²+ 6n-7

tn = Sn - Sn-1

= n²+8n - n²- 6n +7

= 2n + 7n (n²-n²=0)

if,

n=1

2n+7n= 2×1+7×1= 2+7=9

n=2

2×2+7×2= 4+14=18

n=3

2×3 + 7×3= 6+21= 27

Hope it helps ✌️