1 y=cosθ+sinθ=√2(√2/2sinθ+√2/2cosθ)=√2(sinθcosπ/4+cosθsinπ/4)=√2sin(θ+π/4)
因为π/2≤θ≤3π/4,所以3π/4≤θ+π/4≤2π
所以 -√2≤y≤1
2 3象限