(1)、设b=(xcosθ,xsinθ)=(√3,-1）
xsinθ/xcosθ=tanθ=-1/√3
θ=150
(2)、(cosθ,sinθ)(√3,-1）=0
2sin(θ-π/3)=0
x=60
(3)、|2a-b|^2=8-4ab=8-8sin(θ-π/3)
f(min)=4
f(max)=8+4√3