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  1. #1
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    Prove

    Prove that  \bold{u}_{r} \times (\bold{u}_{r} \times \bold{u}_{\theta}) = - \bold{u}_{\theta} .
    Last edited by heathrowjohnny; February 9th 2008 at 06:03 PM.
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  2. #2
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    Quote Originally Posted by heathrowjohnny View Post
    Prove that  \bold{u}_{r} \times (\bold{u}_{r} \times \bold{u}_{\theta}) = - \bold{u}_{\theta} .
    First read the start of this.

    Then substitute \vec{A} = \vec{B} = \bold{u}_{r} and \vec{C} = \bold{u}_{\theta} into the formula.

    Then note that \bold{u}_{r} and \bold{u}_{\theta} are perpendicular and simplify accordingly.
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  3. #3
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    Quote Originally Posted by heathrowjohnny View Post
    Prove that  \bold{u}_{r} \times (\bold{u}_{r} \times \bold{u}_{\theta}) = - \bold{u}_{\theta} .
    i assume that they are vectors, butwhat are the elements? (i forgot them already)

    EDIT: mr f answered it already..
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  4. #4
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    I actually think this is one of those cases where you are using a later result to prove an earlier one. All you have to do, I think, is use the determinant formula.
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