Contact us
Choose a category below so we can get back to you as quickly as possible.
相加得a²;+b²;+c²;+x²;+y²;+z²;=2 (a+x)^2+(b+y)^2+(c+z)^2=2-2ax-2by-2ca>=0 得證
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.