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Math Help - Matrix notation question || and x

  1. #1
    Junior Member
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    Matrix notation question || and x

    I want to calculate the radius of a circle given three points on its perimeter. So I find this formula:
    Circle - Wikipedia, the free encyclopedia

    |P1-P2| |P2-P3| |P3-P1|
    ------------------------- = r
    2 |(P1-P2)x(P2-P3)|

    where the P's are 1 by 3 vectors with x,y,z coordinates of the points 1,2,3.

    What does the "|" mean in the matrix world? Isn't that the length of the vector in geometry?

    And the "x" oepration? Is that matrix multiplication? Then how could that be performed on two 1 by 3 vectors???

    Thankful for clarification!
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  2. #2
    MHF Contributor
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    "|" probably means nothing.

    "|A|", on the other hand, would mean the magnitude of a vector "A".

    "x" indicates a Cross Product.
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