Suppose that a satellite in space, an earth station and the centre of earth all lie in the same plane. Let r be the radius of earth and R be the distance from the centre of earth to the satellite. Let d be the distance from the earth station from the satellite. Let `30^(@)` be the angle of elevation from the earth station to the satellite. if the line segment connecting earth station and satellite subtends angle `alpha` at the centre of earth, then prove that
`d =R sqrt(1 + ((r )/(R))^(2) - 2(r )/(R ) cos alpha)`.

Answer

`d=sqrt(r^(2)/R^(2)+1-(2r)/(R) os alpha)`