Question 356839
a. How many great circles go through the North Pole and the South Pole on the globe?
An infinite number.  Any plane that contains the line between the 2 poles intersects the sphere in a great circle.
-----------------------------------
b. Describe a spherical triangle that has one vertex at the North Pole and the other two vertices on the equator.
The 2 angles on the equator are right angles.  The third can be from >zero to <180 degrees
c. Is there a spherical triangle with three right angles? If so, find one.
As in b above, if the angle at the pole is also 90 degs.
For example, the pole, and longitude 0 degs and 90 degs on the equator.