我认定这件事情是真实的。
wǒ rèndìng zhè jiàn shìqíng shì zhēnshí de 。
I firmly believe that this matter is true.
经过调查，他们认定他是嫌疑犯。
jīngguò diàochá ， tāmen rèndìng tāshì xiányífàn 。
After the investigation, they determined that he was the suspect.
她认定自己会在比赛中获胜。
tā rèndìng zìjǐ huì zài bǐsài zhōng huòshèng 。
She believes firmly that she will win in the competition.