Is a system of equations consistent?

In summary, the given system is consistent with infinitely many solutions. The fourth row becoming 0=0 indicates that X4 is allowed to take on any value, while the rest of the solutions depend on the chosen value of X4. This results in the solutions lying on a line in R^4, indicating one degree of freedom. If there had been two degrees of freedom, the solutions would lie on a plane in R^4.
  • #1
SticksandStones
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Homework Statement


Tell if the given system is consistent or not:
[tex]X_{1} -2X_{4} = -3[/tex]
[tex]2X_{2}+2X_{3} = 0[/tex]
[tex]X_{3}+3X_{4} = 1[/tex]
[tex]-2X_{1}+3X_{2}+2X_{3}+X_{4} = 5[/tex]

Homework Equations


Once put into Reduced Row Echelon Form, the system becomes:
[tex]X_{1}-2X_{4} = -3[/tex]
[tex]X_{2}-3X_{4} = -1[/tex]
[tex]X_{3}+3X_{4} = 1[/tex]

The Attempt at a Solution


I put the system into reduced row echelon form (see above) and can not see a way to find an exact solution to the system so I want to say that it is inconsistent. However, I'm not entirely sure on this matter.

Is it inconsistent?
 
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  • #2
It's consistent, but with infinitely many solutions. The 4th row became 0=0 meaning that X4 is allowed to take on any value it wants and the system will still be consistent. The rest of the solutions depends on what value of x4 is chosen. X4 = 0 gives the solution's {-3,-1,1,0}. Since there is one degree of freedom (ie. one variable that is allowed to do whatever it pleases), the solutions all lie on a line in R^4. If there had been two degrees of freedom, all of the solutions would be on a plane in R^4
 
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  • #3
Vid said:
It's consistent, but with infinitely many solutions. The 4th row became 0=0 meaning that X4 is allowed to take on any value it wants and the system will still be consistent. The rest of the solutions depends on what value of x4 is chosen. X4 = 0 gives the solutions {-3,-1,1,0}. Since there is one degree of freedom (ie. one variable that is allowed to do whatever is pleases), the solutions all lie on a line in R^4. If there had been two degrees of freedom, all of the solutions would be on a plane in R^4

Thank you. That makes far more sense.
 

1. What does it mean for a system of equations to be consistent?

A system of equations is consistent if it has at least one solution that satisfies all of the equations in the system. In other words, the equations in the system do not contradict each other and can be solved simultaneously.

2. How can I tell if a system of equations is consistent?

One way to determine if a system of equations is consistent is by graphing the equations on the same coordinate plane. If the lines intersect at one point, the system is consistent. If the lines are parallel, the system is inconsistent and has no solution. If the lines overlap, the system is consistent and has infinitely many solutions.

3. Can a consistent system of equations have more than one solution?

Yes, a consistent system of equations can have infinitely many solutions. This occurs when the equations in the system are dependent on each other, meaning they are essentially the same equation. In this case, any value that satisfies one equation will also satisfy the other equations, resulting in infinitely many solutions.

4. What happens if a system of equations is inconsistent?

If a system of equations is inconsistent, it means that there is no solution that satisfies all of the equations. This could happen if the equations contradict each other or if there are too many equations in the system. Inconsistent systems are typically represented by parallel lines when graphed.

5. Can a system of equations be both consistent and inconsistent?

No, a system of equations cannot be both consistent and inconsistent. It can only be one or the other. A consistent system has at least one solution, while an inconsistent system has no solution. If a system is inconsistent, it cannot also have a solution.

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