# 德古阿定理

${\displaystyle S_{ABC}^{2}=S_{\color {blue}ABO}^{2}+S_{\color {green}ACO}^{2}+S_{\color {red}BCO}^{2}}$

## 扩展阅读

• Kheyfits, Alexander. The Theorem of Cosines for Pyramids. The College Mathematics Journal (Mathematical Association of America). 2004, 35 (5): 385–388. JSTOR 4146849. Proof of de Gua's theorem and of generalizations to arbitrary tetrahedra and to pyramids.