2nd order differential equations I'm so screwed

In summary, the conversation is discussing the solution to the differential equation uxx + u(x,y) = 0. The attempt at a solution involves factoring u(x,y) into two functions, and using the method of undetermined coefficients to solve the resulting equation. The final solution is a function of y times cos(x) or sin(x).
  • #1
rockymcrockerso
2
0

Homework Statement


Uxx +u(x,y)=0


Homework Equations


?


The Attempt at a Solution



Step 1) u(x,y)=A(x)B(y)
Step 2) uxx=d^u/dx^2
Step 3) d^u/dx^2 + A(x)B(y) = 0
Step 4) d^u/dx^2 = -[A(x)B(y)] (?)

I have no idea what I'm doing, so small words would be useful.
 
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  • #2
You equation is uxx+ u(x,y)= 0?
[tex]\frac{\partial^2u}{\partial x^2}+ u= 0[/tex]

Since there is no differentiation with respect to y, just treat y as a constant. Can you solve u'+u= 0?
 
  • #3
HallsofIvy said:
You equation is uxx+ u(x,y)= 0?
[tex]\frac{\partial^2u}{\partial x^2}+ u= 0[/tex]

Since there is no differentiation with respect to y, just treat y as a constant. Can you solve u'+u= 0?

Yeah I figured it out...it's Acosx+Bsinx...right? (I warned that I don't know what the heck I'm doing).
 
  • #4
Well, sort of, that form times an arbitrary function of y.

Daniel.
 
  • #5
No, not "that form times an arbitrary function of y".

Since y is being treated as a constant, the constants A and B may be functions of y: u(x,y)= f(y)cos(x)+ g(y)sin(x). That is not quite the same thing. For example, f(y)cos(x) satisfies the differential equation but is not a function of y times cos(x)+ sin(x).
 

1. What is a 2nd order differential equation?

A 2nd order differential equation is a mathematical equation that describes the relationship between a function and its derivatives up to the second order. It is commonly used in physics and engineering to model systems that involve acceleration, such as the motion of objects.

2. How is a 2nd order differential equation different from a 1st order differential equation?

A 2nd order differential equation involves a function and its first and second derivatives, while a 1st order differential equation only involves a function and its first derivative. This means that a 2nd order differential equation provides more information about the behavior of the function.

3. Why are 2nd order differential equations important?

2nd order differential equations are important because they can accurately model real-world systems and phenomena. They are used in various fields of science and engineering, such as mechanics, electromagnetism, and thermodynamics, to analyze and predict the behavior of complex systems.

4. Can 2nd order differential equations be solved analytically?

Yes, some 2nd order differential equations can be solved analytically using methods such as separation of variables, substitution, and integration. However, there are many cases where analytical solutions are not possible, and numerical methods must be used instead.

5. How can I approach solving a 2nd order differential equation?

The approach to solving a 2nd order differential equation will depend on the specific equation and its initial conditions. In general, you can start by identifying the type of equation (homogeneous, non-homogeneous, or constant-coefficient) and then applying appropriate techniques and methods to solve it. It is also important to carefully consider the physical meaning of the equation and the behavior of the system being modeled.

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