1.y=(a-8)^2+(b-2)^2+(a-4b)^2+k k你自己算 a=8 b=2 k是最小值
2.两式相加得(x+y)*(x+y+1)=42
3.配平:(x-1)^2+(y+2)^2+(z-3)^2=0
4.(a+b)^2=6ab a