Question

First term and common difference of an A. P are 6 and 3 respectively find sn

Answer 1

Answer:

Step - Step Explanation :

$Given, \\ First \: \: Term = a = 6 \\ Common \: \: Difference = d = 3 \\ \\ Sequence \: \: is : \\ 6, \: \: 9, \: \: 12, \: \: 15, \: \: 18, \: \: 21,... \\ \\ S_{n} = \frac{n}{2}｛2a + (n - 1)d｝ \\ S_{n} = \frac{n}{2} ｛2 \times 6 + (n - 1)3｝ \\ S_{n} = \frac{n}{2} ｛12 + (n - 1)3｝ \\ S_{n} = \frac{n}{2} ｛12 + 3n - 3｝ \\ S_{n} = \frac{n}{2} ｛3n + 9 ｝$