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Solve the initial-value problem. $$t y^{\prime}-y=-1, y(1)=1, t>0$$

Short Answer

Expert verified
The solution is \( y = 1 \).

Step by step solution

01

- Identify the type of differential equation

The given differential equation is: \[ t y^{\text{prime}} - y = -1 \] This is a first-order linear differential equation.
02

- Rewrite the differential equation

Rewrite the equation in the standard form: \[ y^{\text{prime}} - \frac{y}{t} = \frac{-1}{t} \]
03

- Identify the integrating factor

To solve the differential equation, find the integrating factor, \( \mu(t) \): \[ \mu(t) = e^{\int -\frac{1}{t} \, dt} = e^{-\text{ln}|t|} = \frac{1}{t} \]
04

- Multiply through by the integrating factor

Multiply both sides of the equation by the integrating factor \( \frac{1}{t} \):\[ \frac{1}{t} y^{\text{prime}} - \frac{y}{t^2} = -\frac{1}{t^2} \]
05

- Simplify the left-hand side

Recognize that the left-hand side is the derivative of \( \frac{y}{t} \): \[ \frac{d}{dt} \left( \frac{y}{t} \right) = -\frac{1}{t^2} \]
06

- Integrate both sides

Integrate both sides with respect to \( t \): \[ \int \frac{d}{dt} \left( \frac{y}{t} \right) dt = \int -\frac{1}{t^2} dt \] \[ \frac{y}{t} = \frac{1}{t} + C \], where \( C \) is the constant of integration.
07

- Solve for \( y \)

Multiply through by \( t \) to solve for \( y \): \[ y = 1 + Ct \]
08

- Apply the initial condition

Use the initial condition \( y(1) = 1 \) to find \( C \): \[ 1 = 1 + C \cdot 1 \] \[ C = 0 \]
09

- Write the final solution

Substitute \( C = 0 \) into the general solution: \[ y = 1 \]

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Key Concepts

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

First-order linear differential equation
The given problem provides a differential equation of the form:
$$t y^{\text{prime}} - y = -1$$
This is known as a first-order linear differential equation. Let's break it down to understand why.
A first-order linear differential equation is one where the highest derivative of the function (in this case, y) is first-order, meaning it has no higher power than one. Also, it can be written in the standard linear form as:
\[ \frac{dy}{dt} + P(t) y = Q(t) \]
Here, we have:
  • Classify the given equation correctly.
  • Rewrite in the standard form: \( y^{\text{prime}} - \frac{y}{t} = \frac{-1}{t} \).
Recognizing the standard form makes it easier to apply the method of integrating factors to solve it.
This approach is crucial for these types of equations.
Integrating factor
To solve the differential equation, an integrating factor is used.
The integrating factor simplifies the equation, making it easier to solve.
Given the standard form:
  • \( y^{\text{prime}} - \frac{y}{t} = \frac{-1}{t} \)
We identify the integrating factor, \( \mu(t) = e^{\int P(t) dt} \). Here, \( P(t) = -\frac{1}{t} \).
Calculate the integrating factor as:
  • \( \mu(t) = e^{\int -\frac{1}{t} dt} = e^{-ln|t|} = \frac{1}{t} \)
Multiply the differential equation by the integrating factor:
  • \( \frac{1}{t} y^{\text{prime}} - \frac{y}{t^2} = -\frac{1}{t^2} \)
The left-hand side now becomes the derivative of \( \frac{y}{t} \):
\( \frac{d}{dt} \left( \frac{y}{t} \right) = -\frac{1}{t^2} \)
This makes it much easier to integrate both sides.
Constant of integration
Upon integrating both sides of the simplified differential equation, we introduce the constant of integration, \( C \).
Integrating both sides with respect to \( t \):
  • \( \int \frac{d}{dt} \left( \frac{y}{t} \right) dt = \int -\frac{1}{t^2} dt \)
This results in:
  • \( \frac{y}{t} = \frac{1}{t} + C \)
The constant of integration, \( C \), represents an arbitrary constant which we need to solve for using the initial condition provided:
  • \( y(1) = 1 \)
Solving with the initial condition, we get:
  • \( 1 = 1 + C \cdot 1 \)
  • \( C = 0 \)
Finally, the solution to the differential equation is:
  • \( y = 1 \)
Understanding the constant of integration is key to solving initial-value problems accurately.

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