Solve system of equations using laplace transform and evaluate x(1)

In summary, the conversation is about a person struggling to find the correct answer to a system of equations and seeking help from a software called Wolfram. The person uses Cramer's rule and partial fraction decomposition to find the solution, which is then evaluated to be 10492.1. However, the supposed correct answer is -1426.16, which the person finds strange as their solution seems to be correct.
  • #1
davidbenari
466
18

Homework Statement


I keep getting the wrong answer, and wolphram seems to back me up.

Here's the system of equations

##(-10+s)X(s)-7Y(s)=\frac{10}{s}##
##X(s)+(-2+s)Y(s)=0##

Homework Equations

The Attempt at a Solution


Using Cramer's rule I've got

##X(s)=\frac{10}{(s-9)(s-3)}-\frac{20}{s(s-9)(s-3)}##
Using partial fraction decomposition I've got

##x(t)=e^{9t}(10/6-20/54)+e^{3t}(-10/6+20/18)-20/27##

Evaluating ##x(1)## I get ##10492.1##
 
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  • #2
davidbenari said:

Homework Statement


I keep getting the wrong answer, and wolphram seems to back me up.

Here's the system of equations

##(-10+s)X(s)-7Y(s)=\frac{10}{s}##
##X(s)+(-2+s)Y(s)=0##

Homework Equations

The Attempt at a Solution


Using Cramer's rule I've got

##X(s)=\frac{10}{(s-9)(s-3)}-\frac{20}{s(s-9)(s-3)}##
Using partial fraction decomposition I've got

##x(t)=e^{9t}(10/6-20/54)+e^{3t}(-10/6+20/18)-20/27##

Evaluating ##x(1)## I get ##10492.1##

Your answer is correct. What makes you think it is wrong?
 
  • #3
The correct answer is supposedly -1426.16 :/ Strangely enough, if I solve ##y## and evaluate ##y(1)## I get an answer close to that.
 
  • #4
davidbenari said:
The correct answer is supposedly -1426.16 :/ Strangely enough, if I solve ##y## and evaluate ##y(1)## I get an answer close to that.

If you typed out the equations correctly, your solution is correct. So, either you mis-represented the problem, or the supposed answers are wrong.
 
  • Like
Likes davidbenari
  • #5
Thanks for the help.
 

Related to Solve system of equations using laplace transform and evaluate x(1)

1. What is Laplace transform and how does it help solve systems of equations?

Laplace transform is a mathematical tool used to convert a differential equation into an algebraic equation, making it easier to solve. It transforms the equation from the time domain to the frequency domain, where the equations can be manipulated using algebraic techniques.

2. How do you use Laplace transform to solve a system of equations?

To solve a system of equations using Laplace transform, you first take the Laplace transform of each equation in the system. Then, you manipulate the transformed equations using algebraic techniques to eliminate variables and solve for the remaining variables. Finally, you take the inverse Laplace transform to get the solution in the time domain.

3. What is the importance of evaluating x(1) in a system of equations solved using Laplace transform?

Evaluating x(1) means finding the value of the variable x at time t=1. This is important because it gives a specific solution for the system of equations at a specific time, which can be used to understand the behavior of the system over time.

4. Are there any limitations to using Laplace transform to solve systems of equations?

Yes, there are some limitations to using Laplace transform. It is only applicable to linear systems of equations, and the equations must have constant coefficients. Additionally, it can only be used for initial value problems, where the initial conditions of the system are known.

5. Can Laplace transform be used to solve real-world problems?

Yes, Laplace transform can be used to solve real-world problems in various fields such as engineering, physics, and economics. It is particularly useful in solving differential equations that model real-world systems, as it provides an efficient and accurate method to find solutions.

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