Solving Linear ODE: dy/dx-2y=x^2e^2x

  • Thread starter NewtonianAlch
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    Linear Ode
In summary, the given equation is solved using an integrating factor of e^{2x}. After multiplying both sides by the integrating factor and simplifying, the left-hand side is contracted using the chain rule. Integrate both sides and solve for y, the final solution is y = \frac{1}{3}e^{2x}x^{3}+Ce^{2x}.
  • #1
NewtonianAlch
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Homework Statement


Solve [itex]\frac{dy}{dx}[/itex] - 2y = x[itex]^{2}[/itex]e[itex]^{2x}[/itex]

The Attempt at a Solution



Integrating factor = e[itex]^{2x}[/itex]

So we multiply through the given equation by the integrating factor and get:

e[itex]^{2x}[/itex][itex]\frac{dy}{dx}[/itex] - 2e[itex]^{2x}[/itex]y = x[itex]^{2}[/itex]e[itex]^{4x}[/itex]

Contract the left-hand side via the chain rule to get:

[itex]\frac{d}{dx}[/itex](e[itex]^{2x}[/itex]y) = x[itex]^{2}[/itex]e[itex]^{4x}[/itex]

Integrate both sides

e[itex]^{2x}[/itex]y = [itex]\frac{1}{32}e^{4x}[/itex](8x[itex]^{2}[/itex]-4x+1)+C

Now divide through by e[itex]^{2x}[/itex] and the equation definitely does not equal what Wolfram Alpha gives as the solution:

y = [itex]\frac{1}{3}[/itex]e[itex]^{2x}[/itex]x[itex]^{3}[/itex]+Ce[itex]^{2x}[/itex]

I checked some of the parts individually with Wolfram, such as the integration of the right-hand side and that was correct, so I'm not too sure what's causing the difference in answers.
 
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  • #2
Grr, nvm. I forgot the minus sign in the integrating factor -.-
 

Related to Solving Linear ODE: dy/dx-2y=x^2e^2x

1. What is a linear ODE?

A linear ODE (ordinary differential equation) is an equation that involves a function and its derivatives in a linear way. This means that the function and its derivatives appear to the first power and are not multiplied or divided by each other.

2. How do you solve a linear ODE?

To solve a linear ODE, you need to rearrange the equation so that it is in the standard form of dy/dx + P(x)y = Q(x), where P(x) and Q(x) are functions of x. Then, you can use an integrating factor to solve the equation and find the solution for the function y(x).

3. What is the role of the integrating factor in solving linear ODEs?

The integrating factor is a function that is multiplied to both sides of the linear ODE to transform it into a form that can be easily integrated. It is typically determined by the coefficient of y in the standard form of the equation.

4. How do you apply the integrating factor to solve the given equation?

In the equation dy/dx - 2y = x^2e^2x, the integrating factor is e^(-2x). You would multiply both sides of the equation by this integrating factor to get e^(-2x)dy/dx - 2e^(-2x)y = x^2. Then, you can integrate both sides and solve for y(x).

5. Can you use a computer program to solve linear ODEs?

Yes, there are many computer programs and software packages that can solve linear ODEs using numerical methods. These methods involve approximating the solution using a series of points and can be very accurate. However, it is still important to understand the concepts and techniques behind solving linear ODEs by hand.

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