已知曲线C的参数方程为 x=2cost y=2sint(t为参数),曲线C在点(1, 3)处的切线为l,以坐标原点为极点
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x² + y² = 2(cos²t + sin²t) = 2

曲线C为以(0,0)为圆心,半径为√2的圆.

A(1,1),OA的斜率为1,切线l斜率为-1(与x轴的正半轴夹角为3π/4),方程为y - 1 = -(x - 1),y = 2 - x

l与x轴交于B(2,0)

在l上任取一点M(ρ,θ)

OM = ρ,OB = 2,∠BOM = θ,∠MBO = π - 3π/4 = π/4,∠BMO = 3π/4 - θ

按正弦定理:

OM/sin∠MBO = OB/sin∠BMO

ρ/sin(π/4) = 2/sin(3π/4 - θ)

ρ = √2/sin(3π/4 - θ)

以上回答你满意么?