This is the 2058th most frequent German word.
schwachen
"Schwachen" means "to weaken" in English.
Here, 'schwachen' is used as an adjective in the accusative case to describe the noun 'Argumenten', indicating the quality of the arguments as being 'weak'.
Er hat die Aufgabe mit schwachen Argumenten verteidigt.
He defended the task with weak arguments.
In this case, 'schwache' is an adjective in the nominative case describing the feminine noun 'Leistung', expressing that the performance was not strong.
Die Mannschaft zeigte eine schwache Leistung im Spiel.
The team showed a weak performance in the game.
Here, 'schwachen' is used as an adjective in the dative case to describe the plural noun 'Fähigkeiten', referring to the abilities of the people as lacking in strength or competence.