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Math Help - Direction of cross product

  1. #1
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    Direction of cross product

    How do I determine the direction of a cross-product vector. I know it is perpendicular to both of the original vectors used to create the cross product vector. However I am having trouble understanding how to use the right hand rule to determine its direction ie in to page or out of page.
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  2. #2
    Member Danshader's Avatar
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    Hello there,

    Well from what i know lets say you have two vectors A and B and the normal vector to both A and B is N. Let A be a vector pointing 10 o'clock and vector B pointing 3 o'clock.

    For
    AxB
    the direction of the normal vector is downwards (into the paper). To determine the direction use your right fist, since the product is A cross B where A comes first, make it the starting point (knuckles of your fist). Then comes vector B. Use all your fingers(except the thumb) to point from A to B, the thumb show the direction of the normal vector.

    For
    BxA
    the direction is upwards (out of the paper). Using the same method, no we start from B to A (B is the knuckle an A is pointed from B to A using your fingers. Hence from observing the direction in which the thumb show e get the direction of the normal vector.

    Cross product - Wikipedia, the free encyclopedia
    Vector Cross Product - JAVA Interactive Tutorial (this one shows for AxB and the normal vector is C observe how it starts from A and points to B)

    Vector (cross) product (this one gives a good picture of how it is done)

    hope this helps
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