Question

find the sum of first 14 term of AP - 3 - 7 - 11​

Answer 1

Please check to the above solution

Answer 2

The sum of first 14 terms is - 406

Given:

The series is - 3 , - 7 , - 11 , . . .

To find:

The sum of first 14 terms.

Formula to be used:

$S_n = \frac{n}{2} [2a+(n-1)d]$

Solution:

The given series is - 3 , - 7 , - 11 , . . .

We can calculate the sum of first 14 terms by using the following formula,

 $S_n = \frac{n}{2} [2a+(n-1)d]$

n = 14

a = - 3

d = $t_2-t_1$

d = - 7 - ( - 3)

d = - 7 + 3

d = - 4

$S_{14} = \frac{14}{2} [2(-3)+(14-1)(-4)]$

$S_{14} = 7 [-6+(13)(-4)]$

$S_{14} = 7 [-6-52]$

$S_{14} = 7 [-58]$

$S_{14} = - 406$

The sum of first 14 terms is - 406