[alogo] Oblique/Normal Coordinates

Here are some basic relations between oblique/normal coordinates, lengths and areas. (x,y) denote the normal coordinates, resulting by projecting orthogonally to the axes. (x',y') denote the oblique coordinates, resulting by projecting parallel to the axes (for the last formula see AreaThroughDet.html ).

[0_0] [0_1] [0_2] [0_3]
[1_0] [1_1] [1_2] [1_3]
[2_0] [2_1] [2_2] [2_3]

See the file AreaOfPedal.html for a nice application of (2), expressing the other diagonal length of cyclic quadrangle whose a diagonal is a diameter of the circumcircle. This is used also in the discussion on pedals: Pedal.html .

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