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Suppose that the length of a certain organism at age \(t\) is give by \(L(t)\), which satisfies the differential equation $$ \frac{d L}{d t}=e^{-0.1 t}, \quad t \geq 0 $$ Find \(L(t)\) if the limiting length \(L_{\infty}\) is given by $$ L_{\infty}=\lim _{t \rightarrow \infty} L(t)=25 $$ How big is the organism at age \(t=0\) ?

Short Answer

Expert verified
The organism is 15 units long at age \(t=0\).

Step by step solution

01

Understanding the Problem

We need to find the function \(L(t)\) representing the organism's length over time, which is governed by the differential equation \(\frac{dL}{dt} = e^{-0.1t}\). Additionally, we are given that the limiting length as \(t\) approaches infinity is 25, i.e., \(L_{\infty} = 25\). Our task is to integrate this differential equation and find \(L(0)\).
02

Integrate the Differential Equation

We start by integrating the differential equation \(\frac{dL}{dt} = e^{-0.1t}\). The integral of \(e^{-0.1t}\) with respect to \(t\) is \(-10e^{-0.1t} + C\), where \(C\) is the integration constant. Thus, \(L(t) = -10e^{-0.1t} + C\).
03

Apply Limiting Condition

We know that \(L_{\infty} = \lim_{t \to \infty} L(t) = 25\). Applying this condition to our equation \(L(t) = -10e^{-0.1t} + C\), we find that as \(t\) approaches infinity, \(e^{-0.1t}\) approaches zero, so \(L_{\infty} = C = 25\). Thus, the equation simplifies to \(L(t) = -10e^{-0.1t} + 25\).
04

Find L(0)

To find the size of the organism at age \(t = 0\), substitute \(t = 0\) into the equation \(L(t) = -10e^{-0.1t} + 25\). This gives \(L(0) = -10e^{0} + 25 = -10 + 25 = 15\).

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Key Concepts

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

Calculus
Calculus is a branch of mathematics that studies how things change. It's like a special toolset for dealing with quantities that are going through some kind of change or variation. Often, calculus helps us understand and solve problems related to curves and rates of change.

In the context of the differential equation provided, calculus comes into play by allowing us to find the function that describes how the organism's length changes over time. This process involves determining a function, called an *antiderivative*, whose rate of change (derivative) is the given function. The process of reversing the differentiation is called integration, which is a fundamental part of calculus.

Using calculus, we can provide insights into how certain populations grow, how cars accelerate, or even how temperatures change throughout the day. It serves as a bridge between mathematical theory and real-world applications, allowing us to make predictions and understand dynamics in various fields.
Integration
Integration is a method in calculus used to find the antiderivative of a function. Essentially, it is the opposite of differentiation. When we integrate, we are finding a function whose derivative is the one given. In problems involving differential equations, like the one we have for the organism's length, integration is essential to find the function that describes the length over time.

The process of integration can be summarized as follows:
  • Identify the expression you need to integrate.
  • Compute the antiderivative, adding a constant, denoted usually as C.
  • Apply any additional conditions, such as initial values or limits, to solve for the constant C.
In our specific example, we integrated the equation \( \frac{dL}{dt} = e^{-0.1t} \). The integral of this expression is \(-10e^{-0.1t} + C\). This result describes how the organism's length changes with time. Integration thus plays a critical role in finding the solution to the differential equation, nurturing our understanding of the problem.
Limit
Limit is a fundamental concept in calculus that describes the behavior of a function as it approaches a particular point or value. It helps to understand what value a function approaches as the input gets closer to a certain number, or goes to infinity.

In our exercise, the limit provides important information about the organism's ultimate size. The condition \( L_{\infty} = \lim_{t \rightarrow \infty} L(t) = 25 \) indicates that as time goes on indefinitely, the organism will reach a size of 25 units. This approach helps us understand long-term behavior of functions.

Calculating limits in this context involves substituting the point we're interested in studying (in this case, infinity) into the function we've derived. The limit helps confirm or finalize the value of the constant C in our integrated function, thus providing the complete solution to the problem. It's a powerful tool that helps predict trends and final outcomes in various mathematical scenarios.

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Most popular questions from this chapter

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