Question

The sum of first n terms of an AP is given by n²+8n. Find its 12th term?

Answer 1

i hope it will help you

Answer 2

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