Question

Find the sum of the first twelve terms of an A.P whose nth term is 3n+4​

Answer 1

282

Explanation:

To find the sum of arithmetic sequence:

Find the first and last term.

nth term = 3n + 4

First term = a = 3*1 + 4

= 3 + 4

= 7

Last term = l = 3*12 + 4

= 36 + 4

= 40

`\sf \boxed{\bf S_n = (n)/(2)(a +l)}`

`\sf = (12)/(2)(7 + 40)\\\\ =(12)/(2)*47\\\\ = 6 * 47\\\\ = 282`