Verbseoul.
하다 verb (adj)
근면하다geunmyeonhadadiligent, industrious, hardworking

To say diligent, industrious, hardworking politely in the present tense, use 근면해요 (geun-myuhn-hae-yoh). Below is the full conjugation of 근면하다 across the three tenses and three everyday speech levels.

Conjugation table

TenseCasual (반말)Polite (요)Formal (합니다)
Present
근면해
geun-myuhn-hae
근면해요
geun-myuhn-hae-yoh
근면합니다
geun-myuhn-hahm-nee-dah
Past
근면했어
geun-myuhn-hae-ssuh
근면했어요
geun-myuhn-hae-ssuh-yoh
근면했습니다
geun-myuhn-hae-sseum-nee-dah
Future
근면할 거야
geun-myuhn-hahl- -guh-yah
근면할 거예요
geun-myuhn-hahl- -guh-yae-yoh
근면할 겁니다
geun-myuhn-hahl- -guhm-nee-dah

Other useful forms

Command Polite (세요)
근면하세요
geun-myuhn-hah-sae-yoh
Suggestion / Let's Polite (요)
근면해요
geun-myuhn-hae-yoh
Question Polite (요)
근면해요?
geun-myuhn-hae-yoh-?
Connective “and” — (고)
근면하고
geun-myuhn-hah-goh
Conditional “if” — (면)
근면하면
geun-myuhn-hah-myuhn
Noun form — (기)
근면함
geun-myuhn-hahm