1. The problem statement, all variables and given/known data A certain quasar recedes from the earth with a speed of .87c. a jet of material is ejjected towards the earth at .55c relative to the quasar. find speed of ejected material relative to the earth 2. Relevant equations u = u'+v / 1 + u'v/c^2 3. The attempt at a solution guessing. that if I draw both reference frames, v is the velocity that stays constant. in this case v=.87c. in one reference frame, the quasar is receding, and in the other the earth is receding from the quasar. either way there is a .87c and I will call it v. u is the velocity in the reference frame that it is given. .55c is the velocity of the ejected material in the quasar's reference frame. I want it in the Earth's reference frame though, so I call the known velocity in the quasar's reference frame u and the unknown velocity in the earth's reference frame u'. and as long as I keep my signs straight, this should work right? scratch that. the signs on u and v must be from the same reference frame.