F(x,y,z)=x+2y+2z+a(x^2+y^2+z^2-1)
分别对x,y,z求导
1+2ax=0
2+2ay=0
2+2az=0
2x=y=z
x^2+y^2+z^2=1
当x=1/3 y=2/3 z=2/3时
x+2y+2z有最大值=3
|a-1|比x+2y+2z的最大值还大
|a-1|≥3
a>=4 OR a