Solving Characteristic Equation: y'''-y''+y'-y=0

In summary, the conversation discusses solving for the roots of a characteristic equation, specifically one with the equation y'''- y''+y'-y=0. The speaker has already found the real root of 1 by factoring out r, but is unsure how to find the complex roots. By inspection, they determine that r=1 is a root, and to find the other roots they should factor (r-1) from the equation and solve the resulting quadratic. The speaker also mentions the option of using long division or using Wolfram Alpha to factor the equation.
  • #1
newtomath
37
0
I am stuck on solving for the roots of a charactristic equation:

y'''- y''+y'-y=0

where I set r^3-r^2+r-1=0 and factored out r to get r*[ r^2-r +1] -1 =0 to get the real root of 1. How can I solve for the compex roots?
 
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  • #2
By inspection, r = 1 is a root of your characteristic equation.
In order to find the other roots, you should factor (r - 1) from the char. eq.
 
  • #3
So what I would do is write:
[tex]
(r-1)(ar^{2}+br+c)=r^{3}-r^{2}+r-1
[/tex]
Expand and equate coefficients, then solve the quadratic
 
  • #4
hunt_mat said:
So what I would do is write:
[tex]
(r-1)(ar^{2}+br+c)=r^{3}-r^{2}+r-1
[/tex]
Expand and equate coefficients, then solve the quadratic
Typically people use long division. But in this case it's obvious that the other factor is r^2+1.

Or you could just go to Wolfram Alpha and say "factor r^3-r^2+r-1" :-)
 
Last edited:
  • #5
I never really understood long division.
 
  • #6
Got it now, thanks
 

Related to Solving Characteristic Equation: y'''-y''+y'-y=0

1. What is a characteristic equation in relation to solving differential equations?

A characteristic equation is an equation that is used to find the roots or solutions of a differential equation. In the case of solving the equation y'''-y''+y'-y=0, the characteristic equation would be r^3-r^2+r-1=0.

2. How do you solve a characteristic equation?

To solve a characteristic equation, you would typically use algebraic methods to factor the equation and find the roots. In some cases, you may also need to use the quadratic formula or other methods to find the roots.

3. Can you solve a characteristic equation using numerical methods?

Yes, it is possible to solve a characteristic equation using numerical methods such as the Newton-Raphson method or the bisection method. These methods involve using a computer program to approximate the roots of the equation.

4. Why is solving the characteristic equation important in differential equations?

Solving the characteristic equation allows us to find the general solution of a differential equation. This is important because it gives us a complete understanding of the behavior of the system described by the equation and allows us to make predictions about its future behavior.

5. Are there any specific techniques for solving characteristic equations?

Yes, there are some specific techniques that can be used to solve certain types of characteristic equations. For example, if the equation has repeated roots, we can use the method of reduction of order. If the equation has complex roots, we can use the method of undetermined coefficients. Other techniques include the method of variation of parameters and the method of Laplace transforms.

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