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    i think i may be over complicating this but how do i verify that
    5i+3k is parallel to -3i+5k ?

    thanks
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    it's not

    Two vectors are parallel when one of them is ai+bj+ck and the other λ(ai+bj+ck)

    where λ is a real number
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    Wow I've never understood that!! Thanks.
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    Isn't it using the dot product?

    a: ni+nj+nk
    b: mi+mj+mk

    Cos θ = (a.b)/|a||b|
    Where a.b = (ni x mi) + (nj x mj) + (nk x mk)

    Since a.b = (5x3)+(-3x5) = 0

    So Cosθ=0
    θ= arccos 0
    θ= 90° ????
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    yeh thats correct theyre perpendicular to each other u can tell by looking at the cross product whcih is =0

    or vectors [a b] and [-b a] are perp..
 
 
 
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