Why is my Cross Product Calculation Resulting in a Negative Value?

[SeannyBoi71]

Hi all,

Just having some trouble understanding a certain example of cross product. It's actually for physics, but figured it belongs in this forum.

In the question I am supposed to cross (dl)y hat with (x₁)x hat.

So I go (0 dl 0) x (x₁ 0 0) = (-x₁dl)z hat. But turns out the answer the computer looking for is the same but without the negative. Wouldn't that be the case if i crossed it backwards, i.e. (x₁)x hat cross (dl) y hat ??

 

[sandy.bridge]

Yes,
$$(0, dl, 0)\times{(}x_1, 0, 0)=-xdl<b>k</b>$$
and
$$(x_1, 0, 0)\times{(}0, dl, 0)=xdl<b>k</b>$$

 

[SeannyBoi71]

Well then if that's the case I'm still confused. Because then my answer should be right.

 

[mathman]

You need to write the question exactly as it presented, since the cross product depends on which comes first.

 

[SeannyBoi71]

Ok, I am thinking that there is an error in the system, because according to the Biot Savart Law it has a dl x r in the numerator, where r = (x1 0 0) and dl = (0 dl 0). So I computed that but yet my answer was wrong.

 

[mathman]

Ok, I am thinking that there is an error in the system, because according to the Biot Savart Law it has a dl x r in the numerator, where r = (x1 0 0) and dl = (0 dl 0). So I computed that but yet my answer was wrong.

Check the computer program specs. Presumably it will tell you how it interprets a cross product for the order in which the vectors are input.