DB is a median (given). It goes from vertex point D to midpoint B.
The point B is the midpoint of segment AC. So B cuts AC into two equal halves: AB and AC Meaning AB = AC
AC = AB+BC ... segment addition postulate AC = AB+AB ... substitution; replace BC with AB (valid because AB = AC) AC = 2*AB 2*AB = AC 2*AB = 50 ... substitution; replace AC with 50 2*AB/2 = 50/2 ... divide both sides by 2 AB = 25 which is the answer
