How to find the opposite side of the Earth?

Good evening fellow friends!

Who rummages in cartography or mathematics, tell me how knowing the coordinates (lat, lon) point on the map (say Rome) to find a point on the opposite side of the Earth (the line from Uryupinsk, through the center of the Earth, and come out the other side). How to find the coordinates of the exit?
July 12th 19 at 16:54
1 answer
July 12th 19 at 16:56
If rough, then the longitude we need to add or subtract 180 degrees (to get from -180 to +180, that is, if the longitude is less than zero, then add 180, if more than zero, then subtract 180)
And have the latitude to change the sign (North to South and Vice versa).
Alex, can you tell us the formula, if you know? I just can not imagine how to translate for example the coordinates may be the center of Moscow in the opposite direction, in order to get the coordinates to use in google maps for example. - samantha26 commented on July 12th 19 at 16:59

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