確かだよ。
Words
確か
(たしか)
sure; certain; positive; definite; reliable; trustworthy; safe; sound; firm; accurate; correct; exact; If I'm not mistaken; If I remember correctly; If I remember rightly
だ
(だ)
be; is; indicates past or completed action; indicates light imperative
よ
(よ)
indicates certainty, emphasis, contempt, request, etc.; used when calling out to someone; used to catch one's breath or get someone's attention; yo!
Kanji
Readings: カク、 コウ、 たし.か、 たし.かめる
Meanings: assurance, firm, tight, hard, solid, confirm, clear, evident