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Math Help - Vector exemple

  1. #1
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    Vector exemple

    Vector exemple-image.jpgHello i kinda got confused on a exemple, it says show that the dioganal (i think it spell so in english) in a romb is ortogonal.
    so i dont get the first part where u say AB is positive then on second parentes AB is negataiv??? Well i think it should be AC•AB=(AB+BC)•(AB-AD) can some1 explain why is it not like i think?
    Last edited by Petrus; December 4th 2012 at 02:10 AM.
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  2. #2
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    Re: Vector exemple

    \underline{BD}=\underline{BA}+\underline{AD}= \underline{AD}+\underline{BA}=\underline{AD}-\underline{AB}
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    Re: Vector exemple

    Ty now i got it but on the third step where does the BC•BC COME FROM?
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  4. #4
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    Re: Vector exemple

    \underline{AD}=\underline{BC}.
    Two vectors are equal if they have the same magnitude and the same direction.
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    Re: Vector exemple

    ok now i got it ty alot
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  6. #6
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    Re: Vector exemple

    Quote Originally Posted by Petrus View Post
    diagonal (i think it spell so in english) in a rhombus is orthogonal.

    Part of the difficulty is notation. Let \vec{u}=\overrightarrow {AD} ~\&~\vec{v}=\overrightarrow {AB} .

    Now the two diagonals are \vec{u}+\vec{v}~\&~\vec{u}-\vec{v}

    Look at (\vec{u}+\vec{v})\cdot(\vec{u}-\vec{v})=\|\vec{u}\|^2-\|\vec{v}\|^2=0
    because in a rhombus the sides have equal lengths .
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