Math Problem Statement

Find y as a function of x if y(0) = 2, y'(0) = 16, y''(0) = 36, y'''(0) = 0, and y^(4) - 12y''' + 36y'' = 0.

Solution

To solve this problem, we need to solve the fourth-order differential equation:

y(4)12y(3)+36y=0y^{(4)} - 12y^{(3)} + 36y'' = 0

with initial conditions:

y(0)=2,y(0)=16,y(0)=36,y(3)(0)=0y(0) = 2, \quad y'(0) = 16, \quad y''(0) = 36, \quad y^{(3)}(0) = 0

Step 1: Solve the Differential Equation

The differential equation y(4)12y(3)+36y=0y^{(4)} - 12y^{(3)} + 36y'' = 0 suggests a constant-coefficient characteristic equation: r412r3+36r2=0r^4 - 12r^3 + 36r^2 = 0

We can factor this as: r2(r212r+36)=0r^2 (r^2 - 12r + 36) = 0

This further factors into: r2(r6)2=0r^2 (r - 6)^2 = 0

Thus, the roots of the characteristic equation are r=0r = 0 (with multiplicity 2) and r=6r = 6 (with multiplicity 2).

Step 2: Form the General Solution

Given the roots, the general solution for y(x)y(x) is: y(x)=(C1+C2x)+(C3+C4x)e6xy(x) = (C_1 + C_2 x) + (C_3 + C_4 x)e^{6x}

Step 3: Apply Initial Conditions

Now, we apply the initial conditions to find C1C_1, C2C_2, C3C_3, and C4C_4.

  1. Using y(0)=2y(0) = 2: y(0)=C1+C3=2y(0) = C_1 + C_3 = 2

  2. Using y(0)=16y'(0) = 16:

    The derivative of y(x)y(x) is: y(x)=C2+(6C3+C4)e6x+6C4xe6xy'(x) = C_2 + (6C_3 + C_4)e^{6x} + 6C_4 x e^{6x}

    At x=0x = 0: y(0)=C2+6C3=16y'(0) = C_2 + 6C_3 = 16

  3. Using y(0)=36y''(0) = 36:

    The second derivative of y(x)y(x) is: y(x)=(6C4+36C3)e6x+36C4xe6xy''(x) = (6C_4 + 36C_3)e^{6x} + 36C_4 x e^{6x}

    At x=0x = 0: [ y''(0) =

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Math Problem Analysis

Mathematical Concepts

Differential Equations
Characteristic Equation
Exponential Functions

Formulas

Characteristic equation r^4 - 12r^3 + 36r^2 = 0
General solution of a fourth-order homogeneous differential equation with constant coefficients

Theorems

Theory of Linear Differential Equations with Constant Coefficients

Suitable Grade Level

Undergraduate