Hi all, I'm trying to teach myself relativity using Sean Carroll's lecture notes. Although this Isn't a homework question I thought this part of the forum was the best place to ask. On page 76 of http://arxiv.org/pdf/gr-qc/9712019, how have they got the first equation in (3.50) from plugging (3.49) into (3.48). I can't understand where some of the terms have gone? I must be missing something. Can someone explain how this has been achieved. Thanks in advance!