IXL - Write a formula for an arithmetic sequence (Algebra 2 practice)

Write an expression to describe the sequence below. Use n to represent the position of a term in the sequence, where n = 1 for the first term.

77, 154, 231, 308, ...

an =

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question

Write an expression to describe the sequence below. Use n to represent the position of a term in the sequence, where n = 1 for the first term.

^–3, ^–2, ^–1, 0, ...

an =

solution

The sequence ^–3, ^–2, ^–1, 0, ... looks like 1, 2, 3, 4, ... except each term is 4 smaller. So, the expression that describes the sequence is n − 4. Check the first four terms:

To find the 1^st term, plug in n = 1.

n − 4 = 1 − 4 = ^–3

To find the 2^nd term, plug in n = 2.

n − 4 = 2 − 4 = ^–2

To find the 3^rd term, plug in n = 3.

n − 4 = 3 − 4 = ^–1

To find the 4^th term, plug in n = 4.

n − 4 = 4 − 4 = 0

The sequence ^–3, ^–2, ^–1, 0, ... is described by the expression n − 4.

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