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Solve the initial value problems. \(t \frac{d y}{d t}+2 y=t^{3}, \quad t>0, \quad y(2)=1\)

Short Answer

Expert verified
The solution to the initial value problem is \( y = \frac{t^3}{5} - \frac{12}{5t^2} \).

Step by step solution

01

Identify the Type of Differential Equation

The given problem is a first-order linear differential equation of the form \( t \frac{dy}{dt} + 2y = t^3 \). It needs to be transformed so it can be solved using an integrating factor.
02

Transform the Equation

Rearrange the equation to the standard linear form \( \frac{dy}{dt} + P(t)y = Q(t) \). Divide all terms by \(t\) to get:\[ \frac{dy}{dt} + \frac{2}{t}y = t^2 \].
03

Determine the Integrating Factor

The integrating factor \( \mu(t) \) is determined by the formula \( \mu(t) = e^{\int P(t) dt} \), where \( P(t) = \frac{2}{t} \). This gives:\[ \mu(t) = e^{\int \frac{2}{t} dt} = e^{2\ln|t|} = t^2 \].
04

Multiply the Differential Equation

Multiply the entire differential equation by the integrating factor \( t^2 \):\[ t^2 \frac{dy}{dt} + 2t y = t^4 \].
05

Rewrite as a Derivative

Notice that the left side of the equation \( t^2 \frac{dy}{dt} + 2t y = \frac{d}{dt}(t^2 y) \). The equation becomes:\[ \frac{d}{dt}(t^2 y) = t^4 \].
06

Integrate Both Sides

Integrate both sides of the equation to solve for \( y \):\[ \int \frac{d}{dt}(t^2 y) \, dt = \int t^4 \, dt \].This yields \( t^2 y = \frac{t^5}{5} + C \).
07

Solve for C Using Initial Conditions

Use the initial condition \( y(2) = 1 \) to solve for the constant \( C \). Substitute \( t = 2 \) and \( y = 1 \) into \( t^2 y = \frac{t^5}{5} + C \):\[ 4 \cdot 1 = \frac{32}{5} + C \].Solve for \( C \) to get \( C = 4 - \frac{32}{5} = \frac{20}{5} - \frac{32}{5} = -\frac{12}{5} \).
08

Write the General Solution

Using the value of \( C \), write the solution as:\[ t^2 y = \frac{t^5}{5} - \frac{12}{5} \].Divide by \(t^2\) to solve for \(y\):\[ y = \frac{t^3}{5} - \frac{12}{5t^2} \].

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Key Concepts

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

Integrating Factor
Solving first-order linear differential equations often involves finding an integrating factor. This technique helps transform a differential equation into a simple exact equation.

An integrating factor is typically denoted by \( \mu(t) \). It's calculated using the equation \( \mu(t) = e^{\int P(t) \, dt} \), where \( P(t) \) is a function derived from rearranging the original equation into standard form: \( \frac{dy}{dt} + P(t) y = Q(t) \).

In the exercise at hand, once the equation is rearranged to \( \frac{dy}{dt} + \frac{2}{t}y = t^2 \), the function \( P(t) \) becomes \( \frac{2}{t} \). By integrating \( \frac{2}{t} \) with respect to \( t \), we get \( \ln|t^2| \), and subsequently, the integrating factor becomes \( t^2 \).

The role of the integrating factor is to multiply through the differential equation, making the left-hand side a derivative. This simplifies the process of solving the equation, transforming it into a much easier integral to handle.
Initial Value Problem
An initial value problem (IVP) involves finding a solution to a differential equation that satisfies a particular initial condition. This is essential because differential equations often have infinitely many solutions.

For the given exercise, the initial condition is \( y(2) = 1 \). This condition helps us determine the specific solution among the possible ones by providing a point on the curve of the solution.

After performing the necessary integrations and transformations using the integrating factor, we arrive at the relation \( t^2 y = \frac{t^5}{5} + C \).

Substituting \( t = 2 \) and \( y = 1 \) helps solve for the constant \( C \), which personalizes the general solution to fit the initial condition, ensuring the solution passes through the point (2, 1).

This step is crucial, as it converts a general solution into a specific one and is integral to the accuracy of modeling scenarios in sciences and engineering.
Differential Equations Solution
Once the integrating factor is applied, and the initial condition is used, the final solution to the differential equation can be found.

The solution process in this exercise illustrates how the integrating factor simplifies solving the equation to derive a specific formula for \( y(t) \).

Ultimately, the goal is to express \( y \) in terms of \( t \). By simplifying \( t^2 y = \frac{t^5}{5} - \frac{12}{5} \) to \( y = \frac{t^3}{5} - \frac{12}{5t^2} \), we find a clear expression of the solution.

This expression describes how \( y \) behaves as a function of \( t \), considering the constraints of the problem. It highlights not only the transformation of the original complex problem into a manageable form but also the incorporation of initial conditions to meet specific criteria.Understanding how to derive this solution reinforces comprehension of the fundamental processes involved in solving linear differential equations.

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Most popular questions from this chapter

Use Euler's method to calculate the first three approximations to the given initial value problem for the specified increment size. Calculate the exact solution and investigate the accuracy of your approximations. Round your results to four decimal places. $$y^{\prime}=2 x y+2 y, \quad y(0)=3, \quad d x=0.2$$

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Suppose that a pearl is sinking in a thick fluid, like shampoo, subject to a frictional force opposing its fall and proportional to its velocity. Suppose that there is also a resistive buoyant force exerted by the shampoo. According to Archimedes' principle, the buoyant force equals the weight of the fluid displaced by the pearl. Using \(m\) for the mass of the pearl and \(P\) for the mass of the shampoo displaced by the pearl as it descends, complete the following steps. a. Draw a schematic diagram showing the forces acting on the pearl as it sinks, as in Figure 9.19. b. Using \(v(t)\) for the pearl's velocity as a function of time \(t\) write a differential equation modeling the velocity of the pearl as a falling body. c. Construct a phase line displaying the signs of \(v^{\prime}\) and \(v^{\prime \prime}\). d. Sketch typical solution curves. e. What is the terminal velocity of the pearl?

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Solve the differential equations. \(x \frac{d y}{d x}+2 y=1-\frac{1}{x}, \quad x>0\)

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