extended vs lengthened

extended and lengthened both are adjectives.

Word	Noun	Adjective	Verb	Adverb
extended	No	Yes	No	No
lengthened	No	Yes	No	No

As adjectives, extended and lengthened are synonyms defined as:

Other synonyms of extended include elongated, prolonged.

extended (adjective)	lengthened (adjective)
fully extended or stretched forth	drawn out or made longer spatially
beyond the literal or primary sense
large in spatial extent or range or scope or quantity
drawn out or made longer spatially
relatively long in duration; tediously protracted