Chapter 9: Problem 59
In Exercises 47-62, write an expression for the apparent \(n\)th term of the sequence. (Assume that \( n \) begins with 1.) \( 1, 3, 1, 3, 1, \dots \)
Short Answer
Expert verified
The formula for the nth term of the sequence is \( a_n = 2 + (-1)^n \)
Step by step solution
01
Identifying the Pattern of the Sequence
Take a look at the given sequence. The sequence is 1, 3, 1, 3, 1, and so on. It is clear that the sequence alternates between the numbers 1 and 3. Specifically, the number 1 appears at the odd-numbered terms, and the number 3 appears at the even-numbered terms.
02
Formulate a Mathematical Expression
The nth term of this sequence can be written in the form of a function of \( n \) that models this alternating pattern between 1 and 3. This function is \( a_n = 2 + (-2)^n \).
03
Verify the Proposed Expression
To confirm if a function is correct, replace \( n \) with the term's position number in the sequence for a few positions, such as \( n = 1, 2, 3, 4 \) and see if the expected sequence values are obtained. At \( n = 1 \), \( a_n = 2 + (-2)^1 = 0. At \( n = 2 \), the expression gives \( a_n = 2 + (-2)^2 = 4 \), and this pattern continues on for the subsequent terms. The pattern does not coincide with the original sequence, which means the proposed expression is incorrect.
04
Re-formulate a Correct Mathematical Expression
Let's retry formulating the expression. A correct function who alternates between 1 and 3 could be \( a_n = 2 + (-1)^n \).
05
Verify the Correctness of the New Expression
Check if the new function gives the correct sequence terms. For \( n = 1, 2, 3, ... \) the function \( a_n = 2 + (-1)^n \) gives: 1, 3, 1, 3, and so on. This matches the original sequence, so the correct function for the nth term of this sequence is indeed \( a_n = 2 + (-1)^n \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Alternating Sequences
An alternating sequence is a type of sequence in which the terms switch between specific values or patterns regularly. For example, in the sequence given in the exercise, the terms alternate between the numbers 1 and 3. This type of sequence can be visually identified through:
- The repetition of different numbers or patterns in a regular way.
- An observation where the sequence clearly changes its value based on whether the term’s position is even or odd.
Sequence Pattern
Identifying a sequence pattern involves looking for a recurring theme or rule that defines how each term relates to its position in the sequence. In the given sequence, the pattern is straightforward:
- The number 1 appears at odd-numbered positions: 1st, 3rd, 5th, etc.
- The number 3 appears at even-numbered positions: 2nd, 4th, 6th, etc.
Sequence Expression
A sequence expression is a formula that describes each term’s value in relation to its position number, known as \( n \). For alternating sequences, expressions often include factors or functions that switch values based on \( n \). In the corrected solution for the exercise, the expression \( a_n = 2 + (-1)^n \) was used.
- The term \((-1)^n\) alternates between -1 and 1 depending on whether \( n \) is odd or even.
- Adding 2 shifts the whole sequence to alternate between 1 and 3.