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    Spherical right triangles, napiers circle
    From: Patrick Stanistreet
    Date: 2004 Jan 28, 07:57 -0800

    I have been going through a book
    Navigational applications of plane and
    spherical trigonometry by Carol
    Congleton, just  trying to learn the math
    background involved.  On a chapter
    concerning spherical right triangles
    are two rules which I would like to
    find a source for their derivation
    or a proof.
    
    Rule 1:  the sine of a part is equal to
    the product of the tangents of the
    adjacent parts.
    
    Rule 2:  the sine of a part is equal to
    the product of the cosines of the
    opposite parts.
    
    Also if anyone knows how Napiers circle
    was derived I would like understand the
    process.
    
    
    

       
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