x,y为实数,证明x*2-xy+y*2>=x+y-1
问题描述：
x,y为实数,证明x*2-xy+y*2>=x+y-1
答
〔（x^2-xy+y^2）-（x+y-1）〕
=(x^2-2x+1）+(y^2-2y+1)+(x^2-2xy+y^2)
=(x-1)^2+(y-1)^2+(x-y)^2>=0