我决定了参加比赛。

Wǒ juédìng le cānjiā bǐsài.

I've decided to participate in the competition.

她决定跟他离婚。

Tā juédìng gēn tā líhūn.

She decided to divorce him.

你要作出这个决定不容易，我会支持你的。

Nǐ yào zuòchū zhège juédìng bù róngyì, wǒ huì zhīchí nǐ de.

It is not easy for you to make this decision. I will support you.