Chapter 13: Problem 6
Compute the first four terms in each sequence. For Exercises \(1-10,\) assume that each sequence is defined for \(n \geq 1 ;\) in Exercises \(11-14,\) assume that each sequence is defined for \(n \geq 0\) $$c_{n}=(-1)^{n}\left(2^{n}\right)$$
Short Answer
Expert verified
The first four terms are -2, 4, -8, 16.
Step by step solution
01
Identify the Formula
The formula for the sequence is given as \( c_n = (-1)^n (2^n) \). This sequence alternates signs based on \( (-1)^n \) and grows in magnitude as \( 2^n \).
02
Calculate the First Term
To find the first term \( c_1 \), substitute \( n = 1 \) into the formula: \[ c_1 = (-1)^1 (2^1) = -2 \].
03
Calculate the Second Term
To find the second term \( c_2 \), substitute \( n = 2 \) into the formula: \[ c_2 = (-1)^2 (2^2) = 4 \].
04
Calculate the Third Term
To find the third term \( c_3 \), substitute \( n = 3 \) into the formula: \[ c_3 = (-1)^3 (2^3) = -8 \].
05
Calculate the Fourth Term
To find the fourth term \( c_4 \), substitute \( n = 4 \) into the formula: \[ c_4 = (-1)^4 (2^4) = 16 \].
06
List the First Four Terms
Now we list the first four terms of the sequence: \( -2, 4, -8, 16 \). This sequence alternates signs and doubles in magnitude.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Alternating Sequences
In mathematics, an alternating sequence is a pattern where the signs of the terms switch back and forth. For instance, positive numbers may alternate with negative ones, or vice versa.
Alternating sequences are characterized by terms like (-1)^n, which ensures that the sign changes with each successive term.
This creates a sequence that can look something like this:
Alternating sequences are characterized by terms like (-1)^n, which ensures that the sign changes with each successive term.
This creates a sequence that can look something like this:
- First term positive
- Second term negative
- Third term positive
- Fourth term negative
Exponential Growth
Exponential growth describes a process where the rate of growth is proportional to the current size, resulting in a rapid increase over time.
In sequences, we see this type of growth when terms involve powers of a constant, such as 2^n. This is important because it shows how quickly values can escalate in terms of their magnitude.
For example, if you start with 1 and repeatedly multiply by 2, you'll observe:
In sequences, we see this type of growth when terms involve powers of a constant, such as 2^n. This is important because it shows how quickly values can escalate in terms of their magnitude.
For example, if you start with 1 and repeatedly multiply by 2, you'll observe:
- 1 becomes 2
- 2 becomes 4
- 4 becomes 8
- 8 becomes 16
Sequence Formula
A sequence formula provides a way to generate the terms in a sequence. In mathematical exercises, being able to understand and manipulate these formulas is key to solving problems.
For the formula given in the original exercise, \( c_n = (-1)^n \cdot (2^n) \), two components are combined:
This foundational understanding is vital in tackling more complex sequences and series, where sequence expressions can model various real-world processes.
For the formula given in the original exercise, \( c_n = (-1)^n \cdot (2^n) \), two components are combined:
- \((-1)^n\) - ensures that terms alternate in sign
- \(2^n\) - causes the magnitude to double with each increasing term
This foundational understanding is vital in tackling more complex sequences and series, where sequence expressions can model various real-world processes.
Term Calculation
Term calculation in sequences requires substituting index values into the sequence formula efficiently. For instance, in the given formula \(c_n = (-1)^n \cdot (2^n)\), each term can be calculated as follows:
- For the first term, \(n=1\), we find \(c_1 = (-1)^1 \times 2^1 = -2\).
- For the second term, \(n=2\), we calculate \(c_2 = (-1)^2 \times 2^2 = 4\).
- For the third term, \(n=3\), substitution gives us \(c_3 = (-1)^3 \times 2^3 = -8\).
- For the fourth term, \(n=4\), it results in \(c_4 = (-1)^4 \times 2^4 = 16\).