Contact us
Choose a category below so we can get back to you as quickly as possible.
用向量做最簡單!要用正余弦定理做需取AB中點E,用余弦定理證cos角CDE等於COS角DEA從而得角CDE等於角DEA既有AB平行CD!
We and our partners use cookies and other technologies to analyze traffic and optimize your experience. View more info and control your cookies settings at any time in our Cookies Policy.