If I am piloting an airplane to prepare for landing, I change the plane's altitude from a meters to c meters, then the expression that represents the distance between two altitudes is given by |a-c| meters, not by |a+c|.
For, example if the altitude of the plane changes from 1000 meters to 500 meters for preparing for landing then the distance between those two altitudes is |1000 - 500| = 500 meters. (Answer)
But using the expression |a+c|, I will get the wrong answer as |1000 + 500| = 1500 meters.
