Verbseoul.
하다 verb (adj)
약하다yakhadato be weak

To say to be weak politely in the present tense, use 약해요 (yah-kae-yoh). Below is the full conjugation of 약하다 across the three tenses and three everyday speech levels.

Conjugation table

TenseCasual (반말)Polite (요)Formal (합니다)
Present
약해
yah-kae
약해요
yah-kae-yoh
약합니다
yah-kahm-nee-dah
Past
약했어
yah-kae-ssuh
약했어요
yah-kae-ssuh-yoh
약했습니다
yah-kae-sseum-nee-dah
Future
약할 거야
yah-kahl- -guh-yah
약할 거예요
yah-kahl- -guh-yae-yoh
약할 겁니다
yah-kahl- -guhm-nee-dah

Other useful forms

Command Polite (세요)
약하세요
yah-kah-sae-yoh
Suggestion / Let's Polite (요)
약해요
yah-kae-yoh
Question Polite (요)
약해요?
yah-kae-yoh-?
Connective “and” — (고)
약하고
yah-kah-goh
Conditional “if” — (면)
약하면
yah-kah-myuhn
Noun form — (기)
약함
yah-kahm