Math Problem Statement

(1-3t)y'-y=0, y(2)=-6

Solution

The given differential equation is:

(13t)dydty=0(1 - 3t) \frac{dy}{dt} - y = 0

and the initial condition is y(2)=6y(2) = -6.

This is a first-order linear differential equation and can be solved using an integrating factor.

Step 1: Rewrite the equation in standard form

The standard form of a first-order linear equation is:

dydt+P(t)y=Q(t)\frac{dy}{dt} + P(t)y = Q(t)

Rewriting the given equation: dydty13t=0\frac{dy}{dt} - \frac{y}{1 - 3t} = 0 dydt+(113t)y=0\frac{dy}{dt} + \left(- \frac{1}{1 - 3t}\right)y = 0 Here, P(t)=113tP(t) = -\frac{1}{1 - 3t}.

Step 2: Find the integrating factor

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

μ(t)=eP(t)dt\mu(t) = e^{\int P(t) dt}

Substitute P(t)=113tP(t) = -\frac{1}{1 - 3t}:

μ(t)=e113tdt\mu(t) = e^{\int -\frac{1}{1 - 3t} dt} Let u=13tu = 1 - 3t, so du=3dtdu = -3 dt, and we get:

μ(t)=e13ln13t\mu(t) = e^{\frac{1}{3} \ln |1 - 3t|} μ(t)=13t1/3\mu(t) = |1 - 3t|^{1/3}

Step 3: Multiply the original equation by the integrating factor

Now multiply both sides of the equation by μ(t)=13t1/3\mu(t) = |1 - 3t|^{1/3}:

13t1/3dydt+13t1/3(113t)y=0|1 - 3t|^{1/3} \frac{dy}{dt} + |1 - 3t|^{1/3} \left(- \frac{1}{1 - 3t}\right) y = 0

The left-hand side becomes the derivative of y(t)13t1/3y(t) |1 - 3t|^{1/3}, so the equation simplifies to:

ddt(y(t)13t1/3)=0\frac{d}{dt} \left( y(t) |1 - 3t|^{1/3} \right) = 0

Step 4: Integrate both sides

Integrating both sides gives:

y(t)13t1/3=Cy(t) |1 - 3t|^{1/3} = C where CC is a constant of integration.

Step 5: Solve for y(t)y(t)

Solving for y(t)y(t):

y(t)=C13t1/3y(t) = \frac{C}{|1 - 3t|^{1/3}}

Step 6: Apply the initial condition y(2)=6y(2) = -6

Substitute t=2t = 2 and y(2)=6y(2) = -6:

6=C13(2)1/3=C51/3=C51/3-6 = \frac{C}{|1 - 3(2)|^{1/3}} = \frac{C}{|-5|^{1/3}} = \frac{C}{5^{1/3}}

So:

C=6×51/3C = -6 \times 5^{1/3}

Final solution:

The solution to the differential equation is:

y(t)=6×51/313t1/3y(t) = \frac{-6 \times 5^{1/3}}{|1 - 3t|^{1/3}}

Would you like more details on any step, or have any questions?

Here are five related questions you can explore:

  1. How do you find the integrating factor for other first-order linear differential equations?
  2. What happens if the initial condition is given at a different point?
  3. How can this method be adapted to non-homogeneous differential equations?
  4. What is the significance of the absolute value in the solution?
  5. How does the solution behave as tt approaches 1/3?

Tip: When solving first-order linear differential equations, always check that your integrating factor is correctly computed; small mistakes here can lead to errors in the solution.

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Math Problem Analysis

Mathematical Concepts

Differential Equations
First-order Linear Differential Equations
Integrating Factor Method

Formulas

Standard form: dy/dt + P(t)y = Q(t)
Integrating factor: μ(t) = e^{∫P(t) dt}
Solution: y(t) = C / |1 - 3t|^{1/3}

Theorems

Integrating Factor Method for First-order Linear Differential Equations

Suitable Grade Level

Undergraduate Calculus