C1：ρcosβ=3
ρ=3/cosβ.
则取3/cosβ=4cosβ
则 cos^2 β=3/4;
cosβ=±√3/2.
∵ρ大于等于0,由ρ=4cosβ,ρ=3/cosβ得
cosβ大于等于0.
则cosβ=√3/2.
β=π/6.
ρ=4cosβ=3/cosβ=2√3.
∴交点的极坐标是(2√3,π/6).