# Thread: Cross Product negative or positive

1. ## Cross Product negative or positive

Just doing some revision, making sure I know how to answer all the questions found on my mock exam paper.

I'm a little lost, trying to work out whether my vector results I J K are positive or negative because I calculate it to be positive but having looked at my exam result sheet it's negative and I checked to see if the exam sheet result was orthogonal and it was, so I must be going wrong somewhere.

Untitled.jpg 11i is read as -11i on my mock exam results, can someone tell me where I'm going wrong? Thanks!

2. Originally Posted by Drunvalo
Just doing some revision, making sure I know how to answer all the questions found on my mock exam paper.

I'm a little lost, trying to work out whether my vector results I J K are positive or negative because I calculate it to be positive but having looked at my exam result sheet it's negative and I checked to see if the exam sheet result was orthogonal and it was, so I must be going wrong somewhere.

Untitled.jpg 11i is read as -11i on my mock exam results, can someone tell me where I'm going wrong? Thanks!
I think (?) you're computing the determinant by using minors and cofactors, but you're missing the "plus/minus" signs between the terms on the right-hand side of your first "equals" sign after the original determinant. I suspect your "minus" signs are lurking there....

3. Code:
|1   3|
|4   1|   =   1*1 - 3*4   =   -11

4. Originally Posted by Subhotosh Khan
Code:
|1   3|
|4   1|   =   1*1 - 3*4   =   -11
mind = blown. Wow, I can't believe I didn't realize that. Thank you, very much.