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Ch. 10 - Sequences and Infinite Series
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Not the one you use?Change textbook
Chapter 10, Problem 10.1.57b

57–60. Heights of bouncing balls A ball is thrown upward to a height of hₒ meters. After each bounce, the ball rebounds to a fraction r of its previous height. Let hₙ be the height after the nth bounce. Consider the following values of hₒ and r.


b. Find an explicit formula for the nth term of the sequence {hₙ}.


h₀ = 20,r = 0.5

Verified step by step guidance
1
Understand that the sequence {hₙ} represents the height of the ball after the nth bounce, where h₀ is the initial height before any bounce.
Recognize that after each bounce, the ball reaches a height that is a fixed fraction r of the previous height, which means the sequence is geometric.
Recall the general formula for the nth term of a geometric sequence: \(h_n = h_0 \times r^n\), where \(h_0\) is the initial term and \(r\) is the common ratio.
Substitute the given values into the formula: \(h_0 = 20\) and \(r = 0.5\), so the explicit formula becomes \(h_n = 20 \times (0.5)^n\).
This formula allows you to find the height after any number of bounces by plugging in the value of n.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Geometric Sequences

A geometric sequence is a sequence of numbers where each term after the first is found by multiplying the previous term by a constant ratio. In this problem, the heights after each bounce form a geometric sequence with initial term h₀ and common ratio r. Understanding this helps in expressing the nth term explicitly.
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Explicit Formula for Sequences

The explicit formula for a geometric sequence allows direct computation of the nth term without finding all previous terms. It is given by hₙ = h₀ * rⁿ, where h₀ is the initial term and r is the common ratio. This formula is essential to find the height after the nth bounce efficiently.
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Exponents and Powers

Exponents represent repeated multiplication of a base number. In the context of geometric sequences, the common ratio is raised to the power of n to find the nth term. Understanding how to work with exponents is crucial for manipulating and interpreting the explicit formula.
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Related Practice
Textbook Question

67–70. Formulas for sequences of partial sums Consider the following infinite series.


b.Find a formula for the nth partial sum Sₙ of the infinite series. Use this formula to find the next four partial sums S₅, S₆, S₇, S₈ of the infinite series.


∑⁽∞⁾ₖ₌₁2⁄[(2k − 1)(2k + 1)]

Textbook Question

{Use of Tech} A savings plan

James begins a savings plan in which he deposits \(100 at the beginning of each month into an account that earns 9% interest annually, or equivalently, 0.75% per month.

To be clear, on the first day of each month, the bank adds 0.75% of the current balance as interest, and then James deposits \)100.


Let Bₙ be the balance in the account after the nᵗʰ payment, where B₀ = \$0.


b.Find a recurrence relation that generates the sequence {Bₙ}.

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Textbook Question

Suppose the sequence {aₙ}⁽∞⁾ₙ₌₀ is defined by the recurrence relation

aₙ₊₁ = ⅓aₙ + 6;a₀ = 3.


b.Explain why {aₙ}⁽∞⁾ₙ₌₀ converges and find the limit.

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Textbook Question

27–34. Working with sequences Several terms of a sequence {aₙ}ₙ₌₁∞ are given.

b. Find a recurrence relation that generates the sequence (supply the initial value of the index and the first term of the sequence).


{1, 2, 4, 8, 16, ......}

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Textbook Question

18–20. Evaluating geometric series two ways Evaluate each geometric series two ways.


b. Evaluate the series using Theorem 10.7.


∑ (k = 0 to ∞) (–2/7)ᵏ

Textbook Question

72–75. {Use of Tech} Practical sequences

Consider the following situations that generate a sequence


b.Find an explicit formula for the terms of the sequence.


Radioactive decay

A material transmutes 50% of its mass to another element every 10 years due to radioactive decay. Let Mₙ be the mass of the radioactive material at the end of the nᵗʰ decade, where the initial mass of the material is M₀ = 20g.

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