Recall that great circles intersect at two different points. How many angles are formed?
Perpendicular great circles form eight right angles.
Practice makes perfect
Let's begin by making a diagram that illustrates the given postulate in plane Euclidean geometry.
Next, let's draw a pair of great circles (lines) on a sphere. We know they will intersect at two different points and so, they will form eight right angles.
Therefore, we can write the following corresponding statement in spherical geometry.
Perpendicular great circles form
eight right angles
