Simple Linear Differential Operator Problem

In summary, the conversation discusses the solution to the equation (D+1)(D-x)(2e^x+cos(x)) and how the correct answer is different from the one provided in the book. It also addresses a misunderstanding and clarifies the steps in solving the equation.
  • #1
sriracha
30
0
1. (D+1)(D-x)(2e^x+cosx)



2. None



3. (D+1)(D-x)(2e^x+cos(x))=D(2e^x-sinx-2xe^x-xcosx)+1(2e^x-sinx-2xe^x-xcosx)=-4e^x+2e^x-xcosx-2cosx+xsinx-sinx

The correct answer is 2e^x(xsinx-3sinx+2xcosx)
 
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  • #2
It is the part that you don't show that is wrong. There is no way that "D"
or "D- 1" can change "2e^x" to "2xe^x". I suggest you do that again.
 
  • #3
HallsofIvy said:
It is the part that you don't show that is wrong. There is no way that "D"
or "D- 1" can change "2e^x" to "2xe^x". I suggest you do that again.

It's (D-x).
 
  • #4
Please open this again as the last poster closed it because he or she misread the equation.
 
  • #5
Yes, I misread the equation. No, I did not "close" this thread.
[itex]D(2e^x+cos(x))= 2e^x- sin(x)[/itex]
[itex]x(2e^x+cos(x))= 2xe^x+ xcos(x)[/itex]

[itex](D- x)(2e^x+ cos(x))= 2e^x- 2xe^x- sin(x)- xcos(x)[/itex]

[itex]D(2e^x- 2xe^x- sin(x)- xcos(x))= 2e^x- 2e^x- 2xe^x- cos(x)- cos(x)+ xsin(x)= -2xe^x- 2cos(x)+ xsin(x)[/itex]

[itex](D+1)(2e^x- 2xe^x- sin(x)- xcos(x))= -2xe^x- 2cos(x)+xsin(x)+ 2e^x- 2xe^x- sin(x)- xcos(x)= 2e^x- 4xe^x- 2cos(x)- sin(x)+ xsin(x)- xcos(x)[/itex]

What you state as the "correct answer" is impossible. You cannot get [itex]e^x[/itex] multiplied by the trig functions.
 
  • #6
Thanks Ivy. This was from the first set of problems on the topic I have worked so I was not sure I was solving it correctly, but looks like I did. The solution in the back of the book must be incorrect. What do the open and closed envelopes next to the threads signify?
 

Related to Simple Linear Differential Operator Problem

What is a simple linear differential operator problem?

A simple linear differential operator problem is a mathematical concept that involves using a linear differential operator to solve a differential equation. The linear operator is a mathematical function that takes a differential equation as its input and produces a new equation as its output. This new equation is easier to solve and can help find the solution to the original differential equation.

What are some examples of simple linear differential operator problems?

Examples of simple linear differential operator problems include finding the solution to a first-order linear differential equation, such as y' = 2xy, or a second-order linear differential equation, such as y'' + 4y' + 3y = 0. These problems can be solved using a linear differential operator, such as the derivative operator D, which takes the derivative of a function, or the differential operator p(D), which multiplies the function by a polynomial p of the derivative operator D.

What are the benefits of using a simple linear differential operator to solve a differential equation?

Using a simple linear differential operator to solve a differential equation has several benefits. It can simplify the equation and make it easier to solve by breaking it down into smaller parts. It can also help find the general solution to the differential equation, which is a function that satisfies the equation for all possible values of the independent variable. Additionally, using a linear differential operator can provide a more efficient and systematic approach to solving differential equations.

What are some common techniques used to solve simple linear differential operator problems?

Some common techniques used to solve simple linear differential operator problems include the method of undetermined coefficients, variation of parameters, and Laplace transforms. These techniques involve manipulating the differential equation using the linear operator and solving for the unknown function or functions. Other techniques, such as separation of variables and integrating factors, may also be used depending on the specific form of the differential equation.

What are some real-life applications of simple linear differential operator problems?

Simple linear differential operator problems have many real-life applications, particularly in fields such as physics, engineering, and economics. They can be used to model various physical phenomena, such as electrical circuits, heat transfer, and population growth. In engineering, they can be used to solve problems related to motion, vibrations, and control systems. In economics, they can be used to analyze supply and demand, economic growth, and stock market trends.

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