p(x,y)a(1,0)b(0,√3)
pa=(1-x,-y)pb=(-x,√3-y)
pa.pb=-x+x^2-√3y+y^2=
1-x-√(3-3x^2)=f(x)
求导数=-1+√3x/√(1-x^2)=0
x=1/2得极值
再将x=-1,x=1,x=1/2分别代入f(x)
-1<=f(x)<=2