圓C圓心為(0,0),半徑為1/2
直線l的方程:xcosθ+ysinθ - cos²θ+sin²θ = 0
圓心與直線的距離d = | - cos²θ+sin²θ |/√(cos²θ+sin²θ) = |sin²θ-cos²θ|
= |[1-cos(2θ)]/2 - [1 + cos(2θ)]/2|
= |-cos(2θ)| = |cos(2θ)|
二者有公共點,則d = |cos(2θ)| ≤ 1/2
-1/2 ≤ cos(2θ) ≤ 1/2
π/3 + 2kπ ≤ 2θ ≤ 2π/3 + 2kπ (k為整數(shù))
π/6 + kπ ≤ θ ≤ π/3 + kπ (k為整數(shù))