Verbseoul.
하다 verb (adj)
무효하다muhyohadaineffective, invalid

To say ineffective, invalid politely in the present tense, use 무효해요 (moo-hyoh-hae-yoh). Below is the full conjugation of 무효하다 across the three tenses and three everyday speech levels.

Conjugation table

TenseCasual (반말)Polite (요)Formal (합니다)
Present
무효해
moo-hyoh-hae
무효해요
moo-hyoh-hae-yoh
무효합니다
moo-hyoh-hahm-nee-dah
Past
무효했어
moo-hyoh-hae-ssuh
무효했어요
moo-hyoh-hae-ssuh-yoh
무효했습니다
moo-hyoh-hae-sseum-nee-dah
Future
무효할 거야
moo-hyoh-hahl- -guh-yah
무효할 거예요
moo-hyoh-hahl- -guh-yae-yoh
무효할 겁니다
moo-hyoh-hahl- -guhm-nee-dah

Other useful forms

Command Polite (세요)
무효하세요
moo-hyoh-hah-sae-yoh
Suggestion / Let's Polite (요)
무효해요
moo-hyoh-hae-yoh
Question Polite (요)
무효해요?
moo-hyoh-hae-yoh-?
Connective “and” — (고)
무효하고
moo-hyoh-hah-goh
Conditional “if” — (면)
무효하면
moo-hyoh-hah-myuhn
Noun form — (기)
무효함
moo-hyoh-hahm