During a normal Apollo mission, the command/service module was undocked from the lunar module using the reaction control system engines on the service module. (Although the command module had some RCS engines, they were only for attitude control, not to provide translation.) However, during Apollo 13, the service module was already jettisoned before the lunar module was undocked. How were the CM and LM able to safely separate without the help of the SM?
This question is part of a series honoring the 50th anniversary of Apollo 13, "NASA's finest hour".