Solving a Cube Problem with Constant Coefficients

In summary, the conversation is about solving the equation y''' + y' + 2y = 0 using the method of constant coefficients. The problem involves dividing r+1 into r^3 + r + 2 and finding the remaining roots in quadratic form. One of the participants suggests noticing that (-1)^3 + (-1) + 2 = 0, which can help in solving the equation. The other participant then proceeds to explain the process of dividing and finding the remaining roots.
  • #1
mathmike
207
0
hi all i have a bit of a problem here, it has to do with completing the cube.

here is the problem

y''' +y' + 2y = 0

i am trying to sove by the methoed of constant coefficients
 
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  • #2
So your characteristic equation is r3+ r+ 2= 0.

One of the things I notice immediately is that (-1)3+ (-1)+ 2= 0. Does that help?
 
  • #3
So how do you divide r+1 into [itex]r^3+r+2[/itex]?

Well r goes into [itex]r^3, r^2[/itex] times right? So that means:

[tex]r^2(r+1)=r^3+r^2[/tex]

and:

[tex](r^3+r+2)-(r^3+r^2)=-r^2+r+2[/tex]

Ok, we got the first one: [itex]r^2[/itex]

Now, how do you divide r+1 into [itex]-r^2+r+2[/itex]

Keep doin' that to get to the quadratic form of the remaining roots, remainder at end is 0 if -1 is a root. You know how to do this right?
 
Last edited:

Related to Solving a Cube Problem with Constant Coefficients

1. What is a cube problem with constant coefficients?

A cube problem with constant coefficients is a type of mathematical problem that involves finding the solution to an equation with a cubic term and coefficients that do not vary with the independent variable. These problems often require the use of algebraic techniques, such as factoring or the quadratic formula, to find the solution.

2. How do you solve a cube problem with constant coefficients?

To solve a cube problem with constant coefficients, you can use a variety of techniques such as factoring, the quadratic formula, or completing the square. The key is to manipulate the equation so that the cubic term is isolated on one side and the remaining terms can be easily solved for the variable.

3. What are some common mistakes when solving a cube problem with constant coefficients?

Some common mistakes when solving a cube problem with constant coefficients include forgetting to distribute negative signs, making errors when applying the quadratic formula, and forgetting to account for all possible solutions. It is important to check your work carefully and make sure all steps are correct.

4. Are there any tips for solving cube problems with constant coefficients?

One tip for solving cube problems with constant coefficients is to always check for common factors that can be factored out. Additionally, it can be helpful to rewrite the equation in standard form, with the cubic term first, to make it easier to identify the coefficients. It is also important to carefully follow the order of operations when simplifying the equation.

5. How can solving cube problems with constant coefficients be applied in real life?

Cube problems with constant coefficients can be applied in real life in various fields, such as engineering, physics, and economics. For example, in engineering, these types of problems can be used to model the behavior of materials under stress. In physics, they can be used to calculate the trajectory of a projectile. In economics, they can be used to model supply and demand curves. Overall, solving cube problems with constant coefficients helps to develop critical thinking and problem-solving skills that can be applied in various real-life situations.

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