How to find if a vector is parallel to another

[dark_omen]

Okay, so I have two vectors a = <-6, 9, -3> and b = <2, -3, 1>. How can I test to see if these two vectors are parallel or not?
Thanks

 

[radou]

Vectors a and b are parallel if there exists a real number c such that a=cb. In your case it is pretty obvious.

 

[dark_omen]

What if it is not so obvious like the one I presented. Is there another approach to it (cross product of dot product ??)
Thanks

 

[radou]

Think about the definition of the cross product, and see what happens. Btw, just use axb=det \left(\begin{array}{ccc}\vec{i} &amp; \vec{j} &amp; \vec{k}\\a_{1} &amp; a_{2} &amp; a_{3}\\b_{1} &amp; b_{2} &amp; b_{3}\end{array}\right) for a=cb.