Verbseoul.
하다 verb (adj)
반듯하다bandeuthadato be straight

To say to be straight politely in the present tense, use 반듯해요 (bahn-deu-tae-yoh). Below is the full conjugation of 반듯하다 across the three tenses and three everyday speech levels.

Conjugation table

TenseCasual (반말)Polite (요)Formal (합니다)
Present
반듯해
bahn-deu-tae
반듯해요
bahn-deu-tae-yoh
반듯합니다
bahn-deu-tahm-nee-dah
Past
반듯했어
bahn-deu-tae-ssuh
반듯했어요
bahn-deu-tae-ssuh-yoh
반듯했습니다
bahn-deu-tae-sseum-nee-dah
Future
반듯할 거야
bahn-deu-tahl- -guh-yah
반듯할 거예요
bahn-deu-tahl- -guh-yae-yoh
반듯할 겁니다
bahn-deu-tahl- -guhm-nee-dah

Other useful forms

Command Polite (세요)
반듯하세요
bahn-deu-tah-sae-yoh
Suggestion / Let's Polite (요)
반듯해요
bahn-deu-tae-yoh
Question Polite (요)
반듯해요?
bahn-deu-tae-yoh-?
Connective “and” — (고)
반듯하고
bahn-deu-tah-goh
Conditional “if” — (면)
반듯하면
bahn-deu-tah-myuhn
Noun form — (기)
반듯함
bahn-deu-tahm