The task in question is as follows: given N points on a coordinate plane, for some point A find the furthest point (manhattan disrtance) from A in the given set of N points. I know that one of the solutions to this problem is to consider only 4 points, the one with maximal (x + y) value, maximal (x — y) value, maximal (-x — y) value, maximal (y — x) value. It is guaranteed that one of these 4 points will be the furthest point from A. I can see that by doing this we maximize all of the 4 cases of the manhattan distance formula, but when we insert these 4 points into the formula it is not guaranteed that the corresponding cases we want to maximize will hold. Can anyone help me understand why this solution works?