解由x=1+cosa y=sina
则x-2y
=1+cosa-2sina
=1+√5(1/√5cosa-2/√5sina)
=1+√5cos(a+θ)(cosθ=1/√5,sinθ=2/√5)
≤1+√5
故当cos(a+θ)=1时,x-2y有最大值1+√5
解由x=1+cosa y=sina
则x-2y
=1+cosa-2sina
=1+√5(1/√5cosa-2/√5sina)
=1+√5cos(a+θ)(cosθ=1/√5,sinθ=2/√5)
≤1+√5
故当cos(a+θ)=1时,x-2y有最大值1+√5