拖拉滑杆，看看黃色部份的面積。[br]a, b 和 c 有甚麼關係？

Acknowledgement: Adapted from "[url=https://ggbm.at/MJWHp9en]Proof Without Words[/url]" by [url=https://www.geogebra.org/stevephelps]Steve Phelps[/url].