Can you solve this system of simultaneous equations?

  • Context: High School 
  • Thread starter Thread starter physior
  • Start date Start date
  • Tags Tags
    Simultaneous equations
Click For Summary

Discussion Overview

The discussion revolves around a system of three simultaneous linear equations involving three unknowns (x, y, z) and integer coefficients (a, b, c, d, e, f, g, h, i). Participants explore the conditions under which non-trivial solutions exist, specifically addressing the role of the determinant of the coefficient matrix.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the only solution to the system is the trivial solution (x, y, z = 0) or if non-trivial solutions exist.
  • Another participant states that the existence of non-trivial solutions depends on the determinant of the coefficient matrix being zero.
  • There is confusion regarding the terminology, with some participants clarifying that the coefficients refer to the integers (a, b, c, etc.), while others emphasize the importance of understanding the determinant in relation to the coefficients.
  • It is noted that if the determinant is non-zero, the only solution is the trivial one, while a zero determinant indicates the possibility of infinitely many solutions.
  • Participants emphasize the need for knowledge of linear algebra to fully grasp the implications of the determinant on the solutions of the equations.

Areas of Agreement / Disagreement

Participants generally agree on the importance of the determinant in determining the nature of the solutions, but there is disagreement regarding the understanding of terms and the implications of the coefficients and their arrangement in the matrix.

Contextual Notes

There is a lack of clarity regarding the definitions of coefficients and variables, leading to some confusion in the discussion. The relationship between the determinant and the solutions remains a focal point of contention.

physior
Messages
182
Reaction score
1
hello!

I am really wondering what is going on here

let's say we have 3 equations:
with x, y, z to be our unknowns and the rest regular integers

a*x+b*y-c*z=0
d*x-e*y+f*z=0
g*x+h*y+i*z=0

the signs of each integer may be positive or negative

is there a solution to this system of equations or the only solution is x, y, z = 0 ?

thanks!
 
Physics news on Phys.org
It depends on the values of the coefficients.
If the 3 by 3 determinant of the coefficients is zero there are non-trivial solutions. See "homogeneous system of equation" for more details.
 
what you mean "If the 3 by 3 determinant of the coefficients is zero there are non-trivial solutions"?
all the three coefficients are normal integers, either positive or negative
 
physior said:
what you mean "If the 3 by 3 determinant of the coefficients is zero there are non-trivial solutions"?
all the three coefficients are normal integers, either positive or negative

You may need to learn a little linear algebra to understand solutions to these equations. Basically, if you arrange your integer coefficients into a 3x3 matrix and your variables into a vector (x, y, z), then you have matrix/vector equation.

If the matrix has an inverse, then the only solution is (0, 0, 0).

If, however, the matrix has no inverse, then you will have infinitely many solutions.

PS: A matrix has an inverse iff its determinant is non-zero.
 
physior said:
what you mean "If the 3 by 3 determinant of the coefficients is zero there are non-trivial solutions"?
all the three coefficients are normal integers, either positive or negative
Yes, but the determinant of a matrix is a single special quantity, a single number, which is computed from the 9 individual coefficients a - i and their location in the matrix.

See http://en.wikipedia.org/wiki/Determinant

What you are calling coefficients (apparently x, y, and z) from the context of your reply, are actually the unknowns or the variables.
 
no, by coefficients I mean a,b,c,...
 
Then you have 9 coefficients for the system.
The matrix of the coefficients is
a b c
d e f
g h i

The determinant of this matrix tells you if there are other solutions than the trivial (0,0,0).
See the link given above by SteamKing.

The idea is that if the equations are independent there is no simultaneous solution (but zero).
 
Last edited:
physior said:
no, by coefficients I mean a,b,c,...
The there's nine of them in the three equations listed in the OP.
 

Similar threads

  • · Replies 5 ·
Replies
5
Views
2K
Replies
1
Views
10K
  • · Replies 41 ·
2
Replies
41
Views
5K
  • · Replies 17 ·
Replies
17
Views
3K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 1 ·
Replies
1
Views
11K
  • · Replies 1 ·
Replies
1
Views
2K