Question

why three number of geo stationary stallite required for global coverage?why three number of geo stationary stallite required for global coverage?

Answer 1

Three satellites are required for the process known as "Triangulation".

When we receive signal from just one satellite, we will only get an idea of the region in which we are.

If there are two satellites, the intersection of their signals narrows down our location range to a specific plane.

But when there are 3 satellites, their signals intersect at a point uniquely, which is our location.