Log in to add a comment

## Answers

### This Is a Certified Answer

Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.

Sum of first n terms of the AP = n² + 8n

Sum of first 1 term = first term, a = 1² + 8×1 = 9

Sum of first 12 terms = 12² + 8×12 = 240

But we also know that sum of first n terms = (n/2)[a + an]

(an = nth term)

So sum of first 12 terms = (12/2)[9 + a₁₂]

⇒ 240 = 6×(9 + a₁₂)

⇒ 9 + a₁₂ = 240/6 = 40

⇒ a₁₂ = 40- 9

⇒ a₁₂ = 31

12th term is 31.

Sum of first 1 term = first term, a = 1² + 8×1 = 9

Sum of first 12 terms = 12² + 8×12 = 240

But we also know that sum of first n terms = (n/2)[a + an]

(an = nth term)

So sum of first 12 terms = (12/2)[9 + a₁₂]

⇒ 240 = 6×(9 + a₁₂)

⇒ 9 + a₁₂ = 240/6 = 40

⇒ a₁₂ = 40- 9

⇒ a₁₂ = 31

12th term is 31.