# Math Help - how to tell if determinant is negative or positve of 4x4 matrix

1. ## how to tell if determinant is negative or positve of 4x4 matrix

2,3-1,1
-1,0,1,1
2,1,3,-2
1,1,1,-1

Is there any way of quickly determining this?

2. No. Row reductions will tell you soon, but I wouldn't call it "quickly".

3. Originally Posted by lord12
2,3-1,1
-1,0,1,1
2,1,3,-2
1,1,1,-1

Is there any way of quickly determining this?
use expansion method:

$det (A) = a_{i1}A_{i1} + a_{i2}A_{i2} + ... + a_{in}A_{in}$
this is expansion about the ith row..

4. Also, "no". Certainly, it can be determined using a few methods.