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Math Help - Angle between diagonals of a parallelogram

  1. #1
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    Angle between diagonals of a parallelogram

    A parallelogram has its sides determined by OA = (5,1) and OB = (-1,4), determine the angle between the two diagonals of this parallelogram.

    Assuming I have the diagonal vectors going from bottom left to top right and bottom right to top left, the two vectors I'd end up with would be (4,5) and (-6,3), right?

    From there do I use the dot product? I get a different answer than the book, which states it as 77.9
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  2. #2
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    Quote Originally Posted by IanCarney View Post
    A parallelogram has its sides determined by OA = (5,1) and OB = (-1,4), determine the angle between the two diagonals of this parallelogram.
    Assuming I have the diagonal vectors going from bottom left to top right and bottom right to top left, the two vectors I'd end up with would be (4,5) and (-6,3), right?
    From there do I use the dot product? I get a different answer than the book, which states it as 77.9
    If you use <4,5>~\&~<6,-3> as the diagonals you will get the same answer as the text.
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  3. #3
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    Quote Originally Posted by Plato View Post
    If you use <4,5>~\&~<6,-3> as the diagonals you will get the same answer as the text.
    Oh, I get it. Thanks!
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