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What is a 15 of the sequence -7, 2, 11, ...?

A. 128
B. 110
C. 136
D. 119

1 Answer

2 votes

Answer:

D. 119

Explanation:

To find the common difference, we take the second term and subtract the first term

2-(-7) = 9

We check by taking the third term and subtracting the second

11-2 = 9

The common difference is 9

The formula for an arithmetic sequence is

an = a1 +d(n-1)

where a1 is the first term, d is the common difference and n is the number of the term in the sequence

a1=-7, d=9 and we are looking for the 15th term so n=15

a15 = -7 +9(15-1)

a15 = -7+9(14)

=-7 +126

= 119

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