Verbseoul.
하다 verb (adj)
광대하다gwangdaehadavast, extensive

To say vast, extensive politely in the present tense, use 광대해요 (gwahng-dae-hae-yoh). Below is the full conjugation of 광대하다 across the three tenses and three everyday speech levels.

Conjugation table

TenseCasual (반말)Polite (요)Formal (합니다)
Present
광대해
gwahng-dae-hae
광대해요
gwahng-dae-hae-yoh
광대합니다
gwahng-dae-hahm-nee-dah
Past
광대했어
gwahng-dae-hae-ssuh
광대했어요
gwahng-dae-hae-ssuh-yoh
광대했습니다
gwahng-dae-hae-sseum-nee-dah
Future
광대할 거야
gwahng-dae-hahl- -guh-yah
광대할 거예요
gwahng-dae-hahl- -guh-yae-yoh
광대할 겁니다
gwahng-dae-hahl- -guhm-nee-dah

Other useful forms

Command Polite (세요)
광대하세요
gwahng-dae-hah-sae-yoh
Suggestion / Let's Polite (요)
광대해요
gwahng-dae-hae-yoh
Question Polite (요)
광대해요?
gwahng-dae-hae-yoh-?
Connective “and” — (고)
광대하고
gwahng-dae-hah-goh
Conditional “if” — (면)
광대하면
gwahng-dae-hah-myuhn
Noun form — (기)
광대함
gwahng-dae-hahm