Hyperbolic geometry

Hyperbolic geometry

 
A quadrilateral is placed on a sphere. Three of the angles, A,C and B are ri...
 
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Hyperbolic geometry discussion
 
christopherruth
A quadrilateral is placed on a sphere. Three of the angles, A,C and B are right angles. The forth, angle D is not known to be a right angle. How does one show that cosD = -sin(AC)sin(AB)?