Chapter 16: Problem 8
Find the general solution and also the singular solution, if it exists. $$ x^{8} p^{2}+3 x p+9 y=0 $$
Short Answer
Expert verified
The singular solution is \( y = -\frac{3}{4}x \); the general solution is \( y = xp - \frac{9}{2x^8} \).
Step by step solution
01
Identify the Type of Differential Equation
The given equation is an implicit differential equation: \( x^8 p^2 + 3xp + 9y = 0 \) where \( p = \frac{dy}{dx} \). Start by recognizing that this is a Clairaut's form, where it can be expressed in the form \( y = xp + f(p) \).
02
Rearrange and Differentiate
Rearrange the equation as if it were derived from the form \( y = xp + f(p) \). Differentiate the equation with respect to \( x \) to replace \( y \) and \( p \) with their expressions. Let's partially differentiate with respect to \( p \): \( 2x^8p + 3x = 0 \).
03
Solve for Singular Solution
Solve the derived equation \( 2x^8p + 3x = 0 \) to find \( p \). Simplifying gives \( x(2x^7p + 3) = 0 \), which implies \( 2x^7p + 3 = 0 \). Solving gives \( p = -\frac{3}{2x^7} \). Substitute this into the original equation to find \( y = -\frac{3}{4}x \). This is the singular solution.
04
Establish General Solution
Return to the original equation and substitute \( y = f(x) = xp + c \), differentiate to find \( p = \frac{dy}{dx} \). Substitute back into the original form of the equation and simplify to express \( y \) in terms of \( x \) and \( c \), using any algebraic manipulation necessary to fully express the solution. The general solution in this form recovers \( y = xp - \frac{9}{2x^8} \), with \( p \) cancelled out from differentiation.
05
Verify Solutions
Check that both the singular and general solutions satisfy the original equation. Substitute \( p = \frac{dy}{dx} \) in both cases back into the original equation \( x^8 p^2 + 3xp + 9y = 0 \) to verify correctness by confirming that both result in valid statements.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Clairaut's Equation
Clairaut's Equation is a special type of differential equation that can be expressed in the form \( y = xp + f(p) \), where \( p = \frac{dy}{dx} \). This type of equation presents a unique structure that allows for distinct solutions: the general solution and the singular solution.
The general format of Clairaut's Equation makes it particularly interesting because it is defined by a linear relation in terms of the derivative \( p \), and functions of \( p \) itself. This form naturally leads to a family of straight-line solutions, characterized by integrating the differential form with respect to \( x \).
The general format of Clairaut's Equation makes it particularly interesting because it is defined by a linear relation in terms of the derivative \( p \), and functions of \( p \) itself. This form naturally leads to a family of straight-line solutions, characterized by integrating the differential form with respect to \( x \).
- General Solution: Derived by manipulating the form \( y = xp + c \) where \( c \) is a constant.
- Singular Solution: Obtained by eliminating \( p \) through differentiation and solving the derived differential form without integrating.
Singular Solution
A singular solution to a differential equation, such as Clairaut's Equation, is a specific solution that cannot be obtained from the general solution. It arises from a special condition inherent in the equation itself.
For the given equation, after differentiating and rearranging, the singular solution is found by solving \( x(2x^7p + 3) = 0 \), leading to \( p = -\frac{3}{2x^7} \). By substituting \( p \) back into the original equation, the unique solution \( y = -\frac{3}{4}x \) emerges.
For the given equation, after differentiating and rearranging, the singular solution is found by solving \( x(2x^7p + 3) = 0 \), leading to \( p = -\frac{3}{2x^7} \). By substituting \( p \) back into the original equation, the unique solution \( y = -\frac{3}{4}x \) emerges.
- Unlike the general solution, which represents a family of lines, the singular solution is a unique curve.
- This solution marks the envelope or boundary, illustrating all potential general solutions.
General Solution
The general solution to Clairaut's Equation represents a family of functions that satisfy the original problem through a parameter, often denoted as \( c \). For the example provided, the general solution arises by considering the structure \( y = xp + c \). Through differentiation and substitution, this resolves to \( y = xp - \frac{9}{2x^8} \).
Characteristics of the general solution include:
Characteristics of the general solution include:
- Encompassing numerous potential solutions, differing by the value of the constant \( c \).
- Representing linear solutions manifesting as straight lines in the plane, or specific trajectories in space.