A communications satellite is in orbit h = 25, 000 km directly above the Earth’s equator. What is the greatest latitude

[answerhappygod]

A communications satellite is in orbit h = 25, 000 km directly
above the Earth’s equator.
What is the greatest latitude α (this is an angle) from which a
signal can travel from the Earth’s surface to the satellite in a
straight line?
The radius of the Earth is R = 6,400 km.
Find your answer in general form first, that is as a formula α =
... with R and h in the right-hand side, then substitute the given
values and calculate.