Proof without words: Cosine Rule (餘弦公式)

Source: Nelsen, R. B. (1993). Proofs without Words - Exercises in Visual Thinking. The Mathematical Association of America.[br][br]GeoGebra 互動數學教室 [url]http://www.geogebra.hk[/url]
– Alex CHIK

Information: Proof without words: Cosine Rule (餘弦公式)