Question

how many satellite are taking to cover the earth and give the reason

Answer 1

Satellites are used for many purposes. Common types include military and civilian Earth observation satellites, communications satellites, navigation satellites, weather satellites, and space telescopes. Space stations and human spacecraft in orbit are also satellites.

Answer 2

if we consdier geostationary statellite then minimum 3 satellite are required. but it also depends on the resolution and the hight of the orbit it is placed in. so on behalf of this we need only 2 satellites which is of very high resolution and kept at very large distance, covering oppostive sides of earth.