Question

9. Find the sum of the first 6 terms of the sequence: –3, 1, 5, 9, . . . options: A) 25 B) 48 C) 42

Answer 1

C) 42

Explanation:

Given is an Arithmetic Sequence, where

First term a = - 3

Common Difference d = 1-(-3)= 4

n = 6

`S_6=? \\ \\ \because \: S_n = (n)/(2) \{2a + (n - 1)d \} \\ \\ \therefore \: S_6 = (6)/(2) \{2 * ( - 3) + (6 - 1)4 \} \\ \\ \therefore \: S_6 = 3 \{ - 6 + 20\} \\ \\ \therefore \: S_6 = 3 * 14 \\ \\ \huge \red{ \boxed{ \therefore \: S_6 = 42}}`

Answer 2

C. 42.

Explanation:

This is an arithmetic sequence with common difference d = 4 and first term a = -3.

Sum of n terms = (n/2)[2a + (n - 1)d]

Sum of six terms = (6/2)[2(-3) + (6 - 1)4]

= 3 * (-6 + 20)

= 42.