ציטירנדיקער פּירוש אויף יונה 4:9

investigate well here means intensely (as in “I am greatly angry” [Jonah 4: 9]). The word well is closely related to the Hebrew word for “good”.

Sefer Yonah ends with a dramatic flair. After Nineveh repents from its evil ways, Yonah travels in anger to the outskirts of the city and waits to see what will happen to it. There, Hashem designates a Kikayon (a leafy plant, see Rashi ad loc.) to provide shade for Yonah. The Navi is elated. However, Hashem then sends a worm to destroy the plant. Once again exposed to the elements, Yonah feels faint and asks for death. At this point, Hashem asks Yonah, “HaHeiteiv Charah Lecha Al HaKikayon,” “Are you so deeply grieved over the Kikayon?,” to which Yonah responds, “Heiteiv Charah Li Ad Mavet,” “I am greatly grieved to death” (Yonah 4:9).