我发现我的手机不见了。

Wǒ fāxiàn wǒde shǒujī bú jiàn le.

I discovered that my cell phone is missing.

我发现他一直在说谎。

Wǒ fāxiàn tā yìzhí zài shuōhuǎng.

I found him lying all the time.

我发现你今天特别开心！

Wǒ fāxiàn nǐ jīntiān tèbié kāixīn!

I found out you were especially happy today!