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stellarik [79]
3 years ago
10

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

Mathematics
2 answers:
Leno4ka [110]3 years ago
8 0

Answer:

C) 42

Step-by-step explanation:

Given is an Arithmetic Sequence, where

First term a = - 3

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

n = 6

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

ZanzabumX [31]3 years ago
5 0

Answer:

C. 42.

Step-by-step 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.

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