Question 193665
statement:  IF  two  angles  are  adjacent,  THEN  they  have  common vertex, and a  common  side.
converse:  IF  two  angles  have  a  common  vertex,  and  a  common  side,  THEN  they  are  adjacent  angles.

Both  original  statement,  and  converse  are  true(  in  this  case  only,  not  usually)
therefore  we  can  write  a  biconditional,

Two  angles  are  adjacent, IF  AND  ONLY  IF,  they  have  a  common  vertex,  and  a  common  side.