solving linear systems of equations

i want to solve the following linear systems:

a)

2y+3x-7z=6
3z+5x-y=10
-4x+y+z=4

b)

2y+3x-7z=6
3z+5x-y=10
-4y-6x+14z=-12

i wrote the following code:

clc
clear
 
A=[3 2 -7; 5 -1 3; -4 1 1]
B=[6;10;4]
%Ax=B, therefore x=B/A
x=B./A
x=linsolve(A,B)
 
 
C=[3 2 -7;5 -1 3;-6 -4 14]
D=[6;10;-12]
%if Cx=D, therefore x=D/C
x=D./C
x=linsolve(C,D)

and it works for the first but not the second, this comes up in the command window anyone know why?

Warning: Matrix is singular to working precision. 
> In q8_2 (line 15) 

x =

   NaN
   NaN
   NaN

[Jan]

@Chloe St John: You have removed 3 of your questions alraedy. This behavior is disliked in the forum, because you do not want to participate in the community but only to consume the help for free. In case that you try to remove your question again, here is a copy:

i want to solve the following linear systems:

a) 2y+3x-7z=6

3z+5x-y=10

-4x+y+z=4

b) 2y+3x-7z=6

3z+5x-y=10

-4y-6x+14z=-12

i wrote the following code:

clc
clear
 
A=[3 2 -7; 5 -1 3; -4 1 1]
B=[6;10;4]
%Ax=B, therefore x=B/A
x=B./A
x=linsolve(A,B)
 
 
C=[3 2 -7;5 -1 3;-6 -4 14]
D=[6;10;-12]
%if Cx=D, therefore x=D/C
x=D./C
x=linsolve(C,D)

and it works for the first but not the second, this comes up in the command window anyone know why?

Warning: Matrix is singular to working precision. 
> In q8_2 (line 15) 

x =

   NaN
   NaN
   NaN

Answer 1

[Torsten]

The matrix C is singular.

Check whether the linear system C*x=D is solvable at all (Remember the rank condition rank (C ) = rank (C,D)).

If it is solvable, you can use x=pinv(C )*D to get a solution.

Note that x=B./A and x=D./C is wrong in your notation ; it must read x=A\B and x=C\D.

Best wishes

Torsten.

Answer 2

[Annapoorna Nyamagoudra]

 2x+3y−z+2w=7;
x+y+z+w=2;
x+y+3z−2w=−6;
x+2y+z−w=-2

[Walter Roberson]

A = [2 3 -1  2
     1 1  1  1
     1 1  3 -2
     1 2  1 -1]

A = 4×4

2 3 -1 2 1 1 1 1 1 1 3 -2 1 2 1 -1

●

b = [7; 2; -6; -2]

b = 4×1

7 2 -6 -2

●

A\b

ans = 4×1

1 0 -1 2

●

Answer 3

[Sumith M]

x-y=2

x+y=4

2x+y=8

[Walter Roberson]

That system is inconsistent.

Add the first two equations. You get 2*x=6 so x=3. Add the first and last equations. You get 3*x=10 which would require that 3*3=10 which fails

Answer 4

[Maria M]

2y+3x-7z=6

3z+5x-y=10

-4x+y+z=4

[Torsten]

Use "mldivide":

https://de.mathworks.com/help/matlab/ref/mldivide.html