Knowing two spreads allows the third to be calculated by solving the associated quadratic formula but, since two solutions are possible, further " triangle spread rules " must be used to select the appropriate one . ( The relative complexity of this process contrasts with the much simpler method of obtaining a supplementary angle of two others .)
12.
In Euclidean geometry, an "'ex-tangential quadrilateral "'is a external angle bisectors ( supplementary angle bisectors ) at the other two vertex angles, and the external angle bisectors at the angles formed where the extensions of opposite sides intersect ( see the figure to the right, where four of these six are dotted line segments ).
13.
That is, for the latitude ( the North / South coordinate ) the magnitude of the angle remains the same but N is changed to S and vice versa, and for the longitude ( the East / West coordinate ) the angle is replaced by its supplementary angle while E is exchanged for W . For example, the antipode of the point in China at ( a few hundred kilometres from Beijing ) is the point in Argentina at ( a few hundred kilometres from Buenos Aires ).
