1. The problem statement, all variables and given/known data Nevermind, got it. Two spaceships approach the Earth from opposite directions. According to an observer on the Earth, ship A is moving at a speed of 0.753c and ship B at a speed of 0.851c. What is the speed of ship A as observed from ship B? Of ship B as observed from ship A? 2. Relevant equations v = (v' + u) / (1+ (v'u)/(c^2)) and so v' = (u - v) / ((vu)/(c^2) - 1) 3. The attempt at a solution u is the speed of A as observed from Earth. v is the speed of B as observed from Earth. v', then, would be the speed of A or B as observed from the other ship. The values 0.753c and 0.851c plugged in, I get 0.2728c = v'. The speed of one ship as observed by the other ship should be greater than either of the ship's speeds as observed on earth. So where am I incorrect?