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Write out the first five terms of the sequence satisfying the following difference equations: a. \(\Delta a_{n}=\frac{1}{2} a_{n}, \quad a_{0}=1\) b. \(\Delta b_{n}=0.015 b_{n}, \quad b_{0}=1000\) c. \(\Delta p_{n}=0.001\left(500-p_{n}\right), \quad p_{0}=10\) d. \(\Delta t_{n}=1.5\left(100-t_{n}\right), \quad t_{0}=200\)

Short Answer

Expert verified
First five terms: a. 1, 1.5, 2.25, 3.375, 5.0625 b. 1000, 1015, 1030.225, 1045.678375, 1061.363550625 c. 10, 10.49, 10.97951, 11.46853049, 11.95706195951 d. 200, 50, 125, 87.5, 105.625

Step by step solution

01

Understand the Difference Equation

The difference equation is given by \( \Delta a_n = a_{n+1} - a_n \), where \( \Delta a_n \) denotes the change in the sequence term between two successive terms. For the equation \( \Delta a_n = \frac{1}{2}a_n \), we need to calculate the consecutive terms starting from \( a_0 = 1 \).
02

Calculate the Terms for Sequence a

Given \( a_0 = 1 \):\- \( a_1 = a_0 + \Delta a_0 = 1 + \frac{1}{2}(1) = 1.5 \)\- \( a_2 = a_1 + \Delta a_1 = 1.5 + \frac{1}{2}(1.5) = 2.25 \)\- \( a_3 = a_2 + \Delta a_2 = 2.25 + \frac{1}{2}(2.25) = 3.375 \)\- \( a_4 = a_3 + \Delta a_3 = 3.375 + \frac{1}{2}(3.375) = 5.0625 \)\Thus, the first five terms are: 1, 1.5, 2.25, 3.375, 5.0625.
03

Calculate the Terms for Sequence b

Given \( b_0 = 1000 \):\- \( b_1 = b_0 + \Delta b_0 = 1000 + 0.015(1000) = 1015 \)\- \( b_2 = b_1 + \Delta b_1 = 1015 + 0.015(1015) = 1030.225 \)\- \( b_3 = b_2 + \Delta b_2 = 1030.225 + 0.015(1030.225) = 1045.678375 \)\- \( b_4 = b_3 + \Delta b_3 = 1045.678375 + 0.015(1045.678375) = 1061.363550625 \)\Thus, the first five terms are: 1000, 1015, 1030.225, 1045.678375, 1061.363550625.
04

Calculate the Terms for Sequence p

Given \( p_0 = 10 \):\- \( p_1 = p_0 + \Delta p_0 = 10 + 0.001(500 - 10) = 10 + 0.49 = 10.49 \)\- \( p_2 = p_1 + \Delta p_1 = 10.49 + 0.001(500 - 10.49) = 10.97951 \)\- \( p_3 = p_2 + \Delta p_2 = 10.97951 + 0.001(500 - 10.97951) = 11.46853049 \)\- \( p_4 = p_3 + \Delta p_3 = 11.46853049 + 0.001(500 - 11.46853049) = 11.95706195951 \)\Thus, the first five terms are: 10, 10.49, 10.97951, 11.46853049, 11.95706195951.
05

Calculate the Terms for Sequence t

Given \( t_0 = 200 \):\- \( t_1 = t_0 + \Delta t_0 = 200 + 1.5(100 - 200) = 50 \)\- \( t_2 = t_1 + \Delta t_1 = 50 + 1.5(100 - 50) = 125 \)\- \( t_3 = t_2 + \Delta t_2 = 125 + 1.5(100 - 125) = 87.5 \)\- \( t_4 = t_3 + \Delta t_3 = 87.5 + 1.5(100 - 87.5) = 105.625 \)\Thus, the first five terms are: 200, 50, 125, 87.5, 105.625.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Sequence Calculation
Understanding how to calculate the sequence is crucial when solving problems involving difference equations. A sequence is a list of numbers arranged in a particular order. Each number in that list is referred to as a term.
To compute the terms, particularly when using difference equations, we make use of initial information and recursive steps given in the problem. Given an initial value, we utilize the formula for change — the difference equation — to find how each term affects the next.
  • Start with the initial term value.
  • Add the computed difference to find the next term.
  • Repeat the process to find subsequent terms.
This method applies to all sequences in the problem, such as calculating the first term and using recursive steps to find the remaining terms. For instance, for sequence 'a', with initial term 1 and recursive change formula of adding half of the current term, the first five terms can be calculated as shown in the original solution. Building each term relies on simple addition and multiplication steps based on the recursive pattern.
Recursive Formulas
Recursive formulas are a fundamental part of sequence calculations, especially in mathematical problems involving difference equations. These formulas allow us to define each term in a sequence based on its predecessors, specifically by using previous terms to achieve subsequent terms.
A recursive formula typically comes in this form:\[x_{n+1} = x_n + f(x_n)\] where \( f(x_n) \) is a function that determines how the sequence changes from one term to the next.

In the context of the original exercises given, each sequence follows a recursive formula:
  • Sequence 'a': \( \Delta a_{n} = \frac{1}{2} a_{n} \).
  • Sequence 'b': \( \Delta b_{n} = 0.015 b_{n} \).
  • Sequence 'p': \( \Delta p_{n} = 0.001(500-p_{n}) \).
  • Sequence 't': \( \Delta t_{n} = 1.5(100-t_{n}) \).
Each function determines how the current term affects the next one, allowing elaborate growth or decay patterns to emerge as you plot out the sequence terms. This recursive element is central to understanding the nature of the relationships between each term in a sequence.
Mathematical Modeling
Mathematical modeling using difference equations is a powerful tool in analyzing and predicting behaviors in various natural and engineered systems. When a sequence is governed by a difference equation, it helps us model real-world scenarios where changes occur incrementally.

Difference equations capture the dynamics of a system by showing how each state (or term in the sequence) evolves from the previous ones based on specified changes. For example, in our problem:
  • Sequence 'a' models a scenario of growth by a fixed percentage, akin to compound interest.
  • Sequence 'b' demonstrates linear growth in an investment scenario or population growth rate.
  • Sequence 'p' might model a delayed reaction or gradual approach to equilibrium, common in chemical reactions or physics systems.
  • Sequence 't' represents oscillation and damping, where a system like temperature or voltage stabilizes.
By translating these mathematical descriptions into real-world applications, we can better understand the anticipated results and underlying dynamics. This predictive power makes mathematical modeling through difference equations invaluable across multiple fields such as economics, physics, biology, and engineering.

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Most popular questions from this chapter

Your grandparents have an annuity. The value of the annuity increases each month as \(1 \%\) interest on the previous month's balance is deposited. Your grandparents withdraw $$\$ 1000$$ each month for living expenses. Currently, they have $$\$ 50,000$$ in the annuity. Model the annuity with a dynamical system. Find the equilibrium value. What does the equilibrium value represent for this problem? Build a numerical solution to determine when the annuity is depleted.

By substituting \(n=0,1,2,3\), write out the first four algebraic equations represented by the following dynamical systems: a. \(a_{n+1}=3 a_{n}, \quad a_{0}=1\) b. \(a_{n+1}=2 a_{n}+6, \quad a_{0}=0\) c. \(a_{n+1}=2 a_{n}\left(a_{n}+3\right), \quad a_{0}=4\) d. \(a_{n+1}=a_{n}^{2}, \quad a_{0}=1\)

For the following problems, find the solution to the difference equation and the equilibrium value if one exists. Discuss the long-term behavior of the solution for various initial values. Classify the equilibrium values as stable or unstable. a. \(a_{n+1}=-a_{n}+2, \quad a_{0}=1\) b. \(a_{n+1}=a_{n}+2, \quad a_{0}=-1\) c. \(a_{n+1}=a_{n}+3.2, \quad a_{0}=1.3\) d. \(a_{n+1}=-3 a_{n}+4, \quad a_{0}=5\)

The following data were obtained for the growth of a sheep population introduced into a new environment on the island of Tasmania. \({ }^{1}\) $$ \begin{array}{l|cccccc} \hline \text { Year } & 1814 & 1824 & 1834 & 1844 & 1854 & 1864 \\ \hline \text { Population } & 125 & 275 & 830 & 1200 & 1750 & 1650 \\ \hline \end{array} $$ Plot the data. Is there a trend? Plot the change in population versus years elapsed after 1814\. Formulate a discrete dynamical system that reasonably approximates the change you have observed.

In 1868 , the accidental introduction into the United States of the cottony- cushion insect (Icerya purchasi) from Australia threatened to destroy the American citrus industry. To counteract this situation, a natural Australian predator, a ladybird beetle (Novius cardinalis), was imported. The beetles kept the insects to a relatively low level. When DDT (an insecticide) was discovered to kill scale insects, farmers applied it in the hope of reducing the scale insect population even further. However, DDT turned out to be fatal to the beetle as well, and the overall effect of using the insecticide was to increase the numbers of the scale insect. Let \(C_{n}\) and \(B_{n}\) represent the cottony-cushion insect and ladybird beetle population levels, respectively, after \(n\) days. Generalizing the model in Problem 4, we have $$ \begin{aligned} &C_{n+1}=C_{n}+k_{1} C_{n}-k_{2} B_{n} C_{n} \\ &B_{n+1}=B_{n}-k_{3} B_{n}+k_{4} B_{n} C_{n} \end{aligned} $$ where the \(k_{i}\) are positive constants. a. Discuss the meaning of each \(k_{i}\) in the predator-prey model. b. What assumptions are implicitly being made about the growth of each species in the absence of the other species? c. Pick values for your coefficients and try several starting values. What is the longterm behavior predicted by your model? Vary the coefficients. Do your experimental results indicate that the model is sensitive to the coefficients? To the starting values? d. Modify the predator-prey model to reflect a predator-prey system in which farmers apply (on a regular basis) an insecticide that destroys both the insect predator and the insect prey at a rate proportional to the numbers present.

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