Question

Find the general solution of the given differential equation. $$ y^{\mathrm{iv}}-8 y^{\prime}=0 $$

Short answer

Question: Determine the general solution of the given differential equation: $$ y^{\mathrm{iv}}-8 y^{\prime}=0 $$ Answer: The general solution of the given differential equation is $$ y(x) = C_1 + C_2 e^{2x} + C_3 x e^{2x} + C_4 x^2 e^{2x}. $$

Step-by-step solution

Identify the differential equation type

The given differential equation is a homogeneous linear ordinary differential equation of order 4: $$ y^{\mathrm{iv}}-8 y^{\prime}=0 $$

Create the characteristic equation

To create the characteristic equation, we need to replace the derivatives with exponentials. For the given equation, we will get: $$ r^4 - 8r = 0 $$

Solve the characteristic equation

We'll now solve the characteristic equation: $$ r^4 - 8r = 0 $$ Factor out r, and we get: $$ r(r^3 - 8) = 0 $$ The first root is clearly \(r_1 = 0\). For the cubic equation \(r^3 - 8 = 0\), rearrange to get: $$ r^3 = 8 $$ Now we find the other three roots: $$ r_{2,3,4} = \sqrt[3]{8} = 2 $$ So, the characteristic roots are \(r_1 = 0\) and \(r_{2,3,4} = 2\)

Construct the general solution

Based on the roots we found in step 3, we can now write the general solution: $$ y(x) = C_1 + C_2 e^{2x} + C_3 x e^{2x} + C_4 x^2 e^{2x} $$ This is the general solution of the given fourth-order homogeneous linear ordinary differential equation.

Key concepts

Characteristic Equation

When faced with a homogeneous linear ordinary differential equation, one of the pivotal steps toward solving it involves formulating what is known as the characteristic equation. This equation translates the differential equation into algebraic terms, leveraging the power of exponentials to simplify the process of finding solutions. In the context of our example, the fourth order differential equation, \( y^{\mathrm{iv}}-8 y^{\prime}=0 \), is transformed by equating the terms involving derivatives to a polynomial with a variable typically denoted as \(r\). This yields the equation \( r^4 - 8r = 0 \).

By solving this polynomial equation, you establish the roots, which correspond to the exponentials in the homogeneous solution to the differential equation. In essence, the characteristic equation acts as a bridge that takes us from a complex differential equation to a more manageable algebraic one, rendering the path to the solution more accessible.

General Solution of Differential Equation

The general solution of a differential equation is a formula that incorporates all possible solutions to the equation. It embodies the complete set of solutions, with the inclusion of arbitrary constants corresponding to the initial conditions of the problem, which are named C₁, C₂, and so on. This variety allows the general solution to be tailored for particular scenarios, where initial values are specified.

For the differential equation in question, once the characteristic equation is solved and the roots are determined, you craft the general solution. This involves constructing a linear combination of functions that are exponential in nature, each raised to the power of a found root, multiplied by these arbitrary constants. In our step by step example, the general solution is expressed as \( y(x) = C_1 + C_2 e^{2x} + C_3 x e^{2x} + C_4 x^2 e^{2x} \), which ultimately encapsulates all possible behaviors of the system represented by the original differential equation.

Fourth-Order Differential Equation

Differential equations vary in complexity, with the order denoting the highest derivative present. A fourth-order differential equation involves the fourth derivative of the unknown function, making it significantly more complicated than its lower-order counterparts. These equations often arise in contexts like beam deflection in engineering and the motion of a vibrating string, embodying complex dynamic systems.

To solve these higher-order equations, we apply methods generalizable across differing orders, starting with the formulation of the characteristic equation, as previously discussed. After determining the roots, the general solution is constructed with respect to these roots. Despite the higher complexity, the structured approach to solving ensures that fourth-order differential equations, such as \( y^{\mathrm{iv}}-8 y^{\prime}=0 \), become tractable, allowing for detailed analysis of intricate physical phenomena.