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Math Help - trig college question

  1. #1
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    Question trig college question

    Hey I need some help with this one.... I'm not to good with my trig rules.

    The question is.

    Let v = (-cos theta, sin theta)
    w = (cos theta, -sin theta)

    Find v.w.

    Thanks heaps
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  2. #2
    o_O
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    Just a direct application of the dot/scalar product:
    \bold{v} \cdot \bold{w} = \left(\bold{v}_{i} \bold{w}_{i}\right) + \left(\bold{v}_{j} \bold{w}_{j}\right)

    where \bold{v} = \left(-\cos \theta \right) \hat{\bold{i}} + \left(\sin \theta \right)\hat{\bold{j}} and \bold{w} = \left(\cos \theta \right) \hat{\bold{i}} + \left(-\sin \theta \right)\hat{\bold{j}}

    Just plug and chug.
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