Math Problem Statement

t(t-4)y’+y=0 y(2)=1

Solution

We have a first-order linear differential equation:

t(t4)dydt+y=0,y(2)=1t(t - 4) \frac{dy}{dt} + y = 0, \quad y(2) = 1

To solve this differential equation, let's first rewrite it in standard linear form:

dydt+1t(t4)y=0\frac{dy}{dt} + \frac{1}{t(t - 4)} y = 0

This is a linear differential equation of the form:

dydt+p(t)y=0,\frac{dy}{dt} + p(t) y = 0,

where p(t)=1t(t4)p(t) = \frac{1}{t(t - 4)}.

Step 1: Find the Integrating Factor

The integrating factor μ(t)\mu(t) is given by:

μ(t)=ep(t)dt=e1t(t4)dt\mu(t) = e^{\int p(t) \, dt} = e^{\int \frac{1}{t(t - 4)} \, dt}

To compute this integral, we use partial fraction decomposition:

1t(t4)=At+Bt4\frac{1}{t(t - 4)} = \frac{A}{t} + \frac{B}{t - 4}

Let's find AA and BB by equating:

1=A(t4)+Bt.1 = A(t - 4) + Bt.

Solving for AA and BB, we get:

  • For t=4t = 4: 1=4BB=141 = 4B \Rightarrow B = \frac{1}{4}
  • For t=0t = 0: 1=4AA=141 = -4A \Rightarrow A = -\frac{1}{4}

Thus:

1t(t4)=14t+14(t4).\frac{1}{t(t - 4)} = -\frac{1}{4t} + \frac{1}{4(t - 4)}.

Now, we integrate:

1t(t4)dt=(14t+14(t4))dt=14lnt+14lnt4+C.\int \frac{1}{t(t - 4)} \, dt = \int \left( -\frac{1}{4t} + \frac{1}{4(t - 4)} \right) \, dt = -\frac{1}{4} \ln |t| + \frac{1}{4} \ln |t - 4| + C.

Simplify the integrating factor:

μ(t)=e14lnt+14lnt4=(t4t)1/4.\mu(t) = e^{-\frac{1}{4} \ln |t| + \frac{1}{4} \ln |t - 4|} = \left( \frac{|t - 4|}{|t|} \right)^{1/4}.

Step 2: Solve the Differential Equation

Now, multiply the differential equation by the integrating factor μ(t)\mu(t):

(t4t)1/4dydt+(t4t)1/41t(t4)y=0.\left( \frac{|t - 4|}{|t|} \right)^{1/4} \frac{dy}{dt} + \left( \frac{|t - 4|}{|t|} \right)^{1/4} \cdot \frac{1}{t(t - 4)} y = 0.

Simplify to find y(t)y(t), and apply the initial condition y(2)=1y(2) = 1.

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Math Problem Analysis

Mathematical Concepts

Differential Equations
First-order Linear Differential Equations
Integrating Factor

Formulas

Integrating factor formula
Partial fraction decomposition

Theorems

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Suitable Grade Level

Advanced undergraduate