Row echelon form

  • Thread starter Chadlee88
  • Start date
  • #1
41
0

Homework Statement


i'm trying to put the 3x3 matrix: [4 2 6]
[ 2 8 2]
[-1 3 1]
into row echelow from.
but i don't know where i'm goin wrong in my row operations. could some1 please tell me where i hav made the mistake.





Homework Equations





The Attempt at a Solution



[4 2 6] [4 2 6 ] [4 2 6]
[2 8 2] r2->r2+2r3 [0 14 4] r3-> 4r3 [0 14 4]
[-1 3 1] [-1 3 1] [-4 12 4]


r3->r3+r1 [4 2 6 ] r3->r3-r2 [4 2 6]
[0 14 4] [0 14 4] :confused:
[0 14 10 [0 0 6]
 

Answers and Replies

  • #2
Office_Shredder
Staff Emeritus
Science Advisor
Gold Member
4,672
669
Divide the second row by 14, then subtract twice the second row from the first row. Figure out the rest from there
 
  • #3
daniel_i_l
Gold Member
867
0
What makes you think that that's wrong? With a few more operations you can get to I (the identity matrix) if that's what you need.
 
  • #4
41
0
??? I'm trying to find the LU decomposition so U is jst an upper triangular matrix and that's what my answer above is. and from the fact that
det(A) = det(LU) = det(L)det(U) = det(U) as det(L) = 1 the determinant of A has to be equal to the determinant of U. i worked out the determinant of A to be 84 but the determinant of U = 4((14x6)-(4x0))-2((0x6)-(4x0))+6((0x0)-(14x0)) = 4x14x6 = 336 which does not equal 84! i still dont' get what i've done wrong :(
 

Related Threads on Row echelon form

  • Last Post
Replies
9
Views
2K
  • Last Post
Replies
3
Views
1K
Replies
5
Views
3K
Replies
7
Views
11K
  • Last Post
Replies
3
Views
873
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
2
Views
1K
Replies
5
Views
2K
Replies
8
Views
3K
Top