4x4 determinant using upper triangular form

[aznkid310]

[SOLVED] 4x4 determinant using upper triangular form

Homework Statement

|2 0 1 4|
|3 2 -4 -2|
|2 3 -1 0|
|11 8 -4 6|

Homework Equations

Ive done this a number of times and i still can't get the answer. I ended up w/ 275, but the answer is suppose to be zero

The Attempt at a Solution

1) 2 * |1 0 0.5 2|
|3 2 -4 -2|
|2 3 -1 0|
|11 8 -4 6|

2) 2* |1 0 0.5 2|
|0 2 -5.5 -8|
|0 3 -2 -4|
|0 8 -9.5 -5|

3) (2)(2)*|1 0 0.5 2|
| 0 1 -2.75 -4|
|0 3 -2 -4|
|0 8 -9.5 -5|

4) (2)(2)*|1 0 0.5 2|
| 0 1 -2.75 -4|
|0 0 6.25 8|
|0 0 12.5 27|

5) (2)(2)(6.25)* |1 0 0.5 2|
|0 1 -2.75 -4|
|0 0 1 (32/25)|
|0 0 0 11|

Determinant = 11*2*2*6.25 = 275

 

[Defennder]

2) 2* |1 0 0.5 2|
|0 2 -5.5 -8|
|0 3 -2 -4|
|0 8 -9.5 -5|

I would double-check your last row carefully for step 2.

 

[aznkid310]

ah i see! Thanks for pointing that out.