一个难题设x,y,z为正实数.试证1/(x^2+2yz)+1/(
设x,y,z为正实数.试证 1/(x^2+2yz)+1/(y^2+2zx)+1/(z^2+2xy)>= 2/(yz+zx+xy)+1/(x^2+y^2+z^2)
设x,y,z为正实数.试证 1/(x^2+2yz)+1/(y^2+2zx)+1/(z^2+2xy)>= 2/(yz+zx+xy)+1/(x^2+y^2+z^2) 证明如下: