<Li> Each point is associated with a unique line, called the polar line of the point, which is the line on the plane through the center of the sphere and perpendicular to the diameter of the sphere through the given point . </Li> <P> As there are two arcs (line segments) determined by a pair of points, which are not antipodal, on the line they determine, three non-collinear points do not determine a unique triangle . However, if we only consider triangles whose sides are minor arcs of great circles, we have the following properties: </P> <Ul> <Li> The angle sum of a triangle is greater than 180 ° and less than 540 ° . </Li> <Li> The area of a triangle is proportional to the excess of its angle sum over 180 ° . </Li> <Li> Two triangles with the same angle sum are equal in area . </Li> <Li> There is an upper bound for the area of triangles . </Li> <Li> The composition (product) of two (orthogonal) line reflections may be considered as a rotation about either of the points of intersection of their axes . </Li> <Li> Two triangles are congruent if and only if they correspond under a finite product of line reflections . </Li> <Li> Two triangles with corresponding angles equal are congruent (i.e., all similar triangles are congruent). </Li> </Ul> <Li> The angle sum of a triangle is greater than 180 ° and less than 540 ° . </Li>

What does all the angles in a triangle add up to