Problem 42 - Calculus

Question

The solution to \(d^{4} y / d x^{4}=0\) is \(\quad\) ( four constants).

Step-by-Step Solution

Answer

The solution is \( y = \frac{C_1 x^3}{6} + \frac{C_2 x^2}{2} + C_3 x + C_4 \).

Step 1: Understand the Given Differential Equation

The differential equation given is \( \frac{d^4 y}{dx^4} = 0 \). This is a fourth-order differential equation. Since it is set to zero, the task is to find a general solution to this equation, which will involve constant coefficients.

Step 2: Integrate the Equation to Reduce Its Order

Since the fourth derivative of \( y \) is zero, integrate both sides with respect to \( x \) to determine the third derivative: \( \frac{d^3 y}{dx^3} = C_1 \), where \( C_1 \) is the first constant from integration.

Step 3: Integrate Again for Second Derivative

Integrate \( \frac{d^3 y}{dx^3} = C_1 \) with respect to \( x \) to get \( \frac{d^2 y}{dx^2} = C_1 x + C_2 \). This introduces the second constant, \( C_2 \).

Step 4: Integrate to Find the First Derivative

Integrate \( \frac{d^2 y}{dx^2} = C_1 x + C_2 \) with respect to \( x \), and you get \( \frac{d y}{dx} = \frac{C_1 x^2}{2} + C_2 x + C_3 \). \( C_3 \) is another constant from integration.

Step 5: Integrate to Find the General Solution

Finally, integrate \( \frac{d y}{dx} = \frac{C_1 x^2}{2} + C_2 x + C_3 \) with respect to \( x \): \( y = \frac{C_1 x^3}{6} + \frac{C_2 x^2}{2} + C_3 x + C_4 \). Here, \( C_4 \) is the fourth and final constant of integration.

Key Concepts

Integration

Integration is a fundamental concept in calculus, used to find an antiderivative or integral of a function. In simpler terms, integration is the reverse process of differentiation. When you integrate a derivative, you "undo" the derivative, which allows you to recover the original function. For a fourth-order differential equation like \( \frac{d^4 y}{dx^4} = 0 \), integration is essential.To tackle this equation, you integrate each derivative step by step to lower the order:

• First, integrate \( \frac{d^4 y}{dx^4} = 0 \) to get \( \frac{d^3 y}{dx^3} = C_1 \).


• Next, integrate \( \frac{d^3 y}{dx^3} = C_1 \), resulting in \( \frac{d^2 y}{dx^2} = C_1 x + C_2 \).


• Continue with \( \frac{d^2 y}{dx^2} = C_1 x + C_2 \), giving you \( \frac{d y}{dx} = \frac{C_1 x^2}{2} + C_2 x + C_3 \).


• Finally, integrate \( \frac{d y}{dx} = \frac{C_1 x^2}{2} + C_2 x + C_3 \) to find \( y = \frac{C_1 x^3}{6} + \frac{C_2 x^2}{2} + C_3 x + C_4 \).

Integration helps reduce the complexity by one order each time, eventually arriving at the general solution.

Constant of Integration

When you integrate a function, particularly an indefinite integral, you often introduce a constant of integration. This constant accounts for all potential constants in a function whose derivative is zero. For example, when differentiating any constant, the result is zero, which means any constant could have been "lost" during differentiation. In our fourth-order differential equation, each time we integrate, a new constant of integration appears:

• After the first integration, we have \( C_1 \) in \( \frac{d^3 y}{dx^3} = C_1 \).


• The second integration introduces \( C_2 \) in \( \frac{d^2 y}{dx^2} = C_1 x + C_2 \).


• The third integration brings \( C_3 \), \( \frac{d y}{dx} = \frac{C_1 x^2}{2} + C_2 x + C_3 \).


• The final integration results in \( C_4 \) in \( y = \frac{C_1 x^3}{6} + \frac{C_2 x^2}{2} + C_3 x + C_4 \).

These constants ensure we account for all functions that could fit the criteria of having derivatives that match the given differential equation.

General Solution

A general solution to a differential equation encompasses all possible solutions. In our case, we started with the equation \( \frac{d^4 y}{dx^4} = 0 \), a fourth-order equation. Each integration we performed added a layer of possible solutions because of the integration constants. This results in a family of solutions, rather than a single, unique answer.The general solution we derived is:

• \( y = \frac{C_1 x^3}{6} + \frac{C_2 x^2}{2} + C_3 x + C_4 \)

This solution contains four arbitrary constants \( C_1, C_2, C_3, \) and \( C_4 \), reflecting the fourth order of the original differential equation. Why are constants here important? Because they allow the solution to adjust to a range of initial conditions or specific cases. Without these constants, the solution would be too rigid and not universally applicable.