How to find the far side of the Earth?

Question

OpenStreetMap

Good evening fellow friends!
Who fumbles in cartography or mathematics, tell me how, knowing the coordinates (lat, lon) of a point on a map (let's say Uryupinsk), find a point on the back side of the Earth (a line leaving Uryupinsk, through the center of the Earth, and exiting from the other side). How to find her exit coordinates?

Answer 1

If it’s rough, then you need to add or subtract 180 degrees to the longitude (to get from -180 to +180, that is, if the longitude is less than zero, then add 180, if it is greater than zero, then subtract 180)
And change the sign of the latitude (north to south and vice versa).