Chapter 7: Problem 34
Find the general solution of the following equations. $$x^{2} \frac{d w}{d x}=\sqrt{w}(3 x+1)$$
Short Answer
Expert verified
A: The general solution is \(w(x)=3\ln{|x|}-\frac{1}{x}+C\).
Step by step solution
01
Separate the variables
Rewrite the given equation in the form of \(\frac{d w}{\sqrt{w}}=\frac{(3x+1)}{x^2}dx\)
$$\frac{d w}{\sqrt{w}}=\frac{(3x+1)}{x^2}dx$$
02
Integrate both sides
Integrate with respect to their respective variables:
$$\int \frac{d w}{\sqrt{w}}=\int \frac{(3x+1)}{x^2}dx$$
03
Solve the left side integral
To integrate the left side, perform a substitution (\(u=w^{1/2}\)):
$$\int \frac{d w}{\sqrt{w}}=2\int u \, d u =u^2+C_{1}=w(x)$$
04
Solve the right side integral
To integrate the right side, divide the expression into two separate fractions and integrate each term:
$$\int \frac{(3x+1)}{x^2}dx = 3\int \frac{1}{x}dx+\int \frac{1}{x^2}dx\\\implies 3\ln{|x|}-\frac{1}{x}+C_{2}$$
05
Equate both sides and solve for w(x)
Now equate both integrals and isolate w(x):
$$w(x)=3\ln{|x|}-\frac{1}{x}+C$$
Where \(C=C_{2}-C_{1}\) is the constant of integration.
Thus, the general solution of the given differential equation is:
$$w(x)=3\ln{|x|}-\frac{1}{x}+C$$
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Separation of Variables
Separation of Variables is a technique used to solve differential equations. It involves rearranging the equation so that each type of variable is isolated on either side of the equation. This is a fundamental skill in solving differential equations effectively. In the given problem, we start with the equation:
- \( x^{2} \frac{d w}{d x} = \sqrt{w}(3x+1) \)
- \( \frac{d w}{\sqrt{w}} = \frac{(3x+1)}{x^2} dx \)
Integration Techniques
Integration is a crucial part of solving differential equations - once variables are separated. We then integrate both sides to find a general solution.
Integrating the Left Side
To integrate the left side \( \int \frac{d w}{\sqrt{w}} \), we perform a substitution. Let \( u = w^{1/2} \), which simplifies the integral to:- \( 2 \int u \, du \), and solving yields \( u^2 + C_1 = w(x) \)
Integrating the Right Side
When integrating the right side \( \int \frac{(3x+1)}{x^2}dx \), split it into two fractions:- \( 3 \int \frac{1}{x}dx + \int \frac{1}{x^2}dx \), resulting in \( 3\ln{|x|} - \frac{1}{x} + C_2 \)
General Solution
The General Solution is the expression that represents all potential solutions of a differential equation. It includes a constant of integration which adjusts to meet any initial conditions.After integrating both sides, we obtain two expressions:
- From the left, \( u^2 = w(x) \)
- From the right, \( 3\ln{|x|} - \frac{1}{x} + C_2 \)
- \( w(x) = 3\ln{|x|} - \frac{1}{x} + C \)