You can
put this solution on YOUR website!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.