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Let $$P(t)=\frac{L}{1+a e^{-k t}}$$ where \(a, k,\) and \(L\) are all positive constants. Establish each statement analytically using calculus. \(\lim _{t \rightarrow \infty} P(t)=L\)

Short Answer

Expert verified
As \( t \to \infty \), \( P(t) \to L \).

Step by step solution

01

Understand the Expression

The function given is \( P(t) = \frac{L}{1 + ae^{-kt}} \). This is a logistic function that models scenarios where growth is initially exponential and then levels off as it approaches a maximum, which is \( L \). Our task is to determine the behavior of \( P(t) \) as \( t \rightarrow \infty \).
02

Analyze the Exponential Term

As \( t \rightarrow \infty \), the term \( e^{-kt} \) tends towards zero because \( k \) is positive, making the exponent \( -kt \) approach negative infinity. Consequently, \( ae^{-kt} \) approaches zero as well.
03

Substitute into the Expression

Given that \( ae^{-kt} \rightarrow 0 \), substitute this limit into the function: \( P(t) = \frac{L}{1 + ae^{-kt}} \rightarrow \frac{L}{1 + 0} = \frac{L}{1} \). Thus, \( P(t) \rightarrow L \) as \( t \rightarrow \infty \).
04

Conclude the Limit

Hence, the limit of \( P(t) \) as \( t \) approaches infinity is \( L \). This shows that the function reaches its upper limit, consistent with the behavior of logistic growth models. Verify this conclusion by analyzing the initial expression and seeing that our substitutions were coherent and valid.

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Key Concepts

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

Logistic Function
A logistic function is a mathematical model that describes how a quantity increases rapidly at first and then slows down, approaching a finite upper limit. This behavior is typical in systems where resources become limited over time. The general form of the logistic function is given by:\[ P(t) = \frac{L}{1 + a e^{-kt}} \]Here, \(L\) represents the maximum population or carrying capacity that the logistic function approaches as time \(t\) becomes large. The parameters \(a\) and \(k\) are positive constants which control the initial value and growth rate, respectively. Logistic functions are commonly used in ecology to model population growth and in other fields, such as economics and epidemiology, to model saturation scenarios.
Thus, the logistic function exhibits predictable long-term behavior, making it a useful tool for understanding systems that stabilize over time.
Asymptotic Behavior
Asymptotic behavior describes the behavior of mathematical functions as inputs become arbitrarily large. For the logistic function \(P(t) = \frac{L}{1 + a e^{-kt}}\), the asymptotic behavior is observed as \(t\) approaches infinity. In this context, we look at what happens to the value of \(P(t)\) over a long period.- As \(t\) grows, the term \(e^{-kt}\) shrinks towards zero because \(e^{-kt}\) is an exponential decay function.- Consequently, the term \(a e^{-kt}\) also tends towards zero, simplifying the logistic function to \(\frac{L}{1} = L\).Therefore, the asymptotic behavior of the logistic function shows its approach to the upper limit \(L\), confirming that the output nears a constant value as \(t\) increases. This simplifies analysis and predictions in real-world applications where long-term stability is a key consideration.
Exponential Decay
Exponential decay is a mathematical concept where quantities decrease at a rate proportional to their current value. In the logistic function, the term \(e^{-kt}\) exhibits exponential decay as \(t\) increases. This term is crucial because it determines how quickly \(P(t)\) approaches its upper limit \(L\).- The base of the natural logarithm \(e\) raised to a negative power results in a rapid decrease toward zero. - Thus, as time progresses, \(e^{-kt}\) becomes negligibly small.This property of exponential decay ensures that the logistic function's growth rate decreases over time, enabling \(P(t)\) to level off. Understanding exponential decay helps differentiate it from exponential growth, providing insight into why growth in a logistic model accelerates initially, then slows and stabilizes.
Analytical Approach
An analytical approach involves using mathematical analysis techniques to solve problems and derive results. In determining the limit \(\lim_{t \to \infty} P(t) = L\), calculus tools such as limits and continuity facilitate understanding the behavior of logistic functions over time.- By analyzing the exponential decay term \(e^{-kt}\), we deduce that \(e^{-kt} \to 0\) as \(t \to \infty\).- Substituting this result into the logistic function, we find that \(P(t)\) simplifies to \(\frac{L}{1} = L\).This analytical method confirms that regardless of specific initial conditions or growth rates, the logistic function tends towards its carrying capacity. Utilizing calculus in this manner provides certainty and mathematical verification for hypotheses about function behavior, supporting their use in predicting real-world scenarios.

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Most popular questions from this chapter

Biology Ring and Benedict \(^{30}\) created a mathematical model of the yield response of cotton to injury by the bollworm. Normalized yield \(y\) (yield with injury divided by yield without injury) was shown to be approximated by \(\ln y=0.1494 \ln x-5.5931 x+7.12 x^{2},\) where \(x\) is the number of injured reproductive organs (flower buds plus capsules) per \(100 .\) Graph on your grapher, and determine the approximate value of \(x\) for which \(y\) attains a maximum on the interval [0,0.05] . Confirm, using calculus.

Production Costs Suarez-Villa and Karlsson \(^{31}\) studiedthe relationship between the sales in Sweden's electronic industry and production costs (per unit value of product sales). Their data is presented in the following table. $$ \begin{array}{|c|ccccc|} \hline x & 7 & 13 & 14 & 15 & 17 \\ \hline y & 0.91 & 0.72 & 0.91 & 0.81 & 0.72 \\ \hline x & 20 & 25 & 27 & 35 & 45 \\ \hline y & 0.90 & 0.77 & 0.65 & 0.73 & 0.70 \\ \hline x & 45 & 63 & 65 & 82 & \\ \hline y & 0.78 & 0.82 & 0.92 & 0.96 & \\ \hline \end{array} $$ Here \(x\) is product sales in millions of krona, and \(y\) is production costs per unit value of product sales. a. Use cubic regression to find the best-fitting cubic to the data. Graph. b. Find where the function is increasing and where it is decreasing. What does this say about economies of scale?

What is the area of the largest rectangle that can be enclosed by a semicircle of radius \(a\) ?

Agriculture Dai and colleagues \(^{16}\) created a mathematical model that showed the yield response of corn in Indiana to soil moisture was approximated by the equation \(y=-2600+2400 x-70 x^{2}+\frac{2}{3} x^{3},\) where \(y\) is measured in bushels per acre and \(x\) is a soil moisture index. Find the value of the soil moisture index on the interval [0,40] that maximizes yield.

Biological Control Lysyk \(^{80}\) studied the effect of temperature on various life history parameters of a parasitic wasp for the purposes of pest management. He constructed a mathematical model given approximately by $$ D(t)=0.00007 t(t-13)(36-t)^{0.4} $$ where \(t\) is temperature in degrees Celsius and \(D\) is the reciprocal of development time in days. Find \(D^{\prime}(t)\). (Hint: You might wish to refer to the formula \((f \cdot g \cdot h)^{\prime}=f^{\prime}\). \(g \cdot h+f \cdot g^{\prime} \cdot h+f \cdot g \cdot h^{\prime}\) found in Exercise 48 of Sec- tion 4.2.) Graph and find where \(D\) attains a maximum.

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