Answer
See answers.
Work Step by Step
a. See diagram. We choose the North Pole as a vertex. The other two vertices are points at the same latitude, on nearly opposite sides of the Earth. The angle at the North Pole is $179^{\circ}$.
b. This task is impossible on a sphere. In order to draw a triangle on a two-dimensional surface where the sum of the angles is less than $180^{\circ}$, a surface with negative curvature is needed (see figure 33–18).
