Chapter 4: Problem 6
First find the general solution (involving a constant C) for the given differential equation. Then find the particular solution that satisfies the indicated condition. (See Example 2.) \(\frac{d y}{d x}=x^{-3}+2 ; y=3\) at \(x=1\)
Short Answer
Expert verified
The particular solution is \(y = -\frac{1}{2} x^{-2} + 2x + \frac{3}{2}\).
Step by step solution
01
Identify the Differential Equation
The differential equation given is \(\frac{d y}{d x}=x^{-3}+2\). Our task is to find the general solution first, which involves integrating each term.
02
Integrate the Differential Equation
Integrate both sides of the equation. For the left-hand side, it becomes \(\int d y = \int (x^{-3} + 2) \, d x\). This results in \(y = \int x^{-3} \, d x + \int 2 \, d x\).
03
Integrate Each Term Separately
First, integrate \(x^{-3}\), which yields \(-\frac{1}{2} x^{-2}\) and integrate \(2\) to obtain \(2x\). Therefore, the integrated left-hand side becomes \(y = -\frac{1}{2} x^{-2} + 2x + C\), where \(C\) is the constant of integration.
04
Write the General Solution
The complete general solution, incorporating the constant \(C\), is \(y = -\frac{1}{2} x^{-2} + 2x + C\).
05
Apply Initial Condition to Find Particular Solution
Use the condition that \(y=3\) when \(x=1\). Substitute \(x=1\) and \(y=3\) into the general solution: \(3 = -\frac{1}{2} (1)^{-2} + 2(1) + C\).
06
Solve for Constant C
Calculate: \(3 = -\frac{1}{2} \times 1 + 2 + C\). This simplifies to \(3 = -\frac{1}{2} + 2 + C\). Thus, \(3 = \frac{3}{2} + C\). Solve for \(C\) to obtain \(C = 3 - \frac{3}{2} = \frac{3}{2}\).
07
Write the Particular Solution
Substitute \(C = \frac{3}{2}\) back into the general solution: \(y = -\frac{1}{2} x^{-2} + 2x + \frac{3}{2}\). This represents the particular solution satisfying the initial condition.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Integration
In solving differential equations, integration plays a pivotal role. When faced with a differential equation like \( \frac{d y}{d x}=x^{-3}+2 \), integration helps us find the antiderivative or the original function. The goal is to reverse the process of differentiation, converting the derivative back into its function.
- **Integrating Individual Terms:** Start by integrating each term separately. Terms like \( x^{-3} \) integrate to \( -\frac{1}{2} x^{-2} \), whereas constants such as \( 2 \) integrate to \( 2x \).
- **Combining Results:** Once each term is integrated, we combine them to form the solution. Also remember to introduce the constant of integration \( C \), which represents any constant that could be added to the antiderivative, since differentiation of a constant results in zero.
Initial Conditions
After obtaining the general solution of a differential equation, initial conditions are used to find a specific, particular solution that fits a given situation. In our exercise, we were given that \( y = 3 \) when \( x = 1 \).
- **Purpose of Initial Conditions:** These conditions help identify a unique solution from the infinite possibilities provided by the general solution. They specify where the solution should pass through, allowing us to calculate the constant \( C \).
- **Using Initial Conditions:** Substitute the provided values into the general solution. This substitution validates the conditions and is used to solve for \( C \).
General Solution
The general solution of a differential equation encompasses all possible solutions. After integrating, we get this form that typically includes an arbitrary constant \( C \).
- **Form of General Solutions:** For our given equation, the general solution looks like: \( y = -\frac{1}{2} x^{-2} + 2x + C \). Here, \( C \) signifies any constant value that could be present, due to indefinite integration.
- **Wide Applicability:** Because it includes \( C \), the general solution is flexible. It represents a family of curves, each corresponding to a different value of \( C \).
Particular Solution
A particular solution is derived from a general solution by applying specific initial conditions, yielding a precise solution that fits a given scenario.
- **Deriving Particular Solutions:** From the general solution \( y = -\frac{1}{2} x^{-2} + 2x + C \), and using the initial condition \( y=3 \) when \( x=1 \), we determine the exact value of \( C \). In this case, \( C = \frac{3}{2} \).
- **Form of the Particular Solution:** With \( C \) known, we substitute back into the general solution to get the particular solution: \( y = -\frac{1}{2} x^{-2} + 2x + \frac{3}{2} \).